| 22 |
stabilized thereafter; while it increased after 2005 by less than 0.5${^\circ}$C in North Greenland. Comparisons with {\it in situ} measurements off the continental shelf in the |
stabilized thereafter; while it increased after 2005 by less than 0.5${^\circ}$C in North Greenland. Comparisons with {\it in situ} measurements off the continental shelf in the |
| 23 |
Labrador and Irminger Seas indicate that the model initial conditions were 0.4${^\circ}$C too warm in the south but the simulated warming is correctly reproduced; while measurements from |
Labrador and Irminger Seas indicate that the model initial conditions were 0.4${^\circ}$C too warm in the south but the simulated warming is correctly reproduced; while measurements from |
| 24 |
the Eastern Baffin Bay reveal that the model initial conditions were 1.0${^\circ}$C too cold in the northwest but the simulated ocean warming brought |
the Eastern Baffin Bay reveal that the model initial conditions were 1.0${^\circ}$C too cold in the northwest but the simulated ocean warming brought |
| 25 |
modeled temperature closer to observations, i.e. the simulated warming is 1.0${^\circ}$C too large. At several key locations, the modeled |
modeled temperature closer to observations, i.e., the simulated warming is 1.0${^\circ}$C too large. At several key locations, the modeled |
| 26 |
oceanic changes off the shelf and below the seasonal mixed layer were rapidly transmitted to the shelf within troughs towards (model-unresolved) fjords. |
oceanic changes off the shelf and below the seasonal mixed layer were rapidly transmitted to the shelf within troughs towards (model-unresolved) fjords. |
| 27 |
Unless blocked in the fjords by shallow sills, these warm subsurface waters had potential to propagate down the fjords and melt the glacier fronts. Based on |
Unless blocked in the fjords by shallow sills, these warm subsurface waters had potential to propagate down the fjords and melt the glacier fronts. Based on |
| 28 |
model sensitivity simulations from an independent study (Xu and others, 2012), we show that the oceanic changes have very likely increased the subaqueous |
model sensitivity simulations from an independent study (Xu and others, 2012), we show that the oceanic changes have very likely increased the subaqueous |
| 41 |
and others, 2011; Howat and others, 2008; Murray and others, 2010; Straneo and others, 2010; Rignot and others, 2010). In Greenland, the vast majority of the ice |
and others, 2011; Howat and others, 2008; Murray and others, 2010; Straneo and others, 2010; Rignot and others, 2010). In Greenland, the vast majority of the ice |
| 42 |
discharged into the ocean is controlled by marine-terminating or tidewater glaciers, i.e., glaciers that terminate in the ocean, melt in contact with the ocean, and |
discharged into the ocean is controlled by marine-terminating or tidewater glaciers, i.e., glaciers that terminate in the ocean, melt in contact with the ocean, and |
| 43 |
calve into icebergs. An increase in the temperature of the subsurface waters at the front of these glaciers would increase the subaqueous melt rates of their calving faces, cause |
calve into icebergs. An increase in the temperature of the subsurface waters at the front of these glaciers would increase the subaqueous melt rates of their calving faces, cause |
| 44 |
retreat of the glacier fronts and yield changes in force balance that could trigger speed up. Floating ice tongues only exist north of 76${^\circ}$N (Rignot and others, 2001). At low latitudes, |
retreat of the glacier fronts, and yield changes in force balance that could trigger speed up. Floating ice tongues only exist north of 76${^\circ}$N (Rignot and others, 2001). At low latitudes, |
| 45 |
Jakobshavn Isbrae (JKS) at 69$^\circ$N was the only glacier that maintained a floating ice tongue until it disintegrated in 2002 (Weidick and others, 2003). Holland and others (2008) attributed |
Jakobshavn Isbrae (JKS) at 69$^\circ$N was the only glacier that maintained a floating ice tongue until it disintegrated in 2002 (Weidick and others, 2003). Holland and others (2008) attributed |
| 46 |
its disintegration to the intrusion of warm Irminger waters into Disko Bay in the mid-1990s. A similar subtropical origin of oceanic heat was suggested by Howat and others (2008), |
its disintegration to the intrusion of warm Irminger waters into Disko Bay in the mid-1990s. A similar subtropical origin of oceanic heat was suggested by Howat and others (2008), |
| 47 |
Straneo and others (2010) and Christoffersen and others (2011) for glaciers that accelerated in the east. |
Straneo and others (2010), and Christoffersen and others (2011) for glaciers that accelerated in the east. |
| 48 |
|
|
| 49 |
The Irminger Waters (IW) found around the margins of southern and western Greenland are named due to their advection through the Irminger Sea, the eastern |
The Irminger Waters (IW) found around the margins of southern and western Greenland are named due to their advection through the Irminger Sea, the eastern |
| 50 |
lobe of the North Atlantic subpolar gyre (SPG). The variability of water mass properties of the IW is related to North Atlantic atmospheric forcing variability (Myers and others, 2007). |
lobe of the North Atlantic subpolar gyre (SPG). The variability of water mass properties of the IW is related to North Atlantic atmospheric forcing variability (Myers and others, 2007). |
| 53 |
cause the SPG to expand which, in turn, reduces the amount of subtropical-origin waters entering the SPG from the North Atlantic Drift. A shift in NAO phase from high to low |
cause the SPG to expand which, in turn, reduces the amount of subtropical-origin waters entering the SPG from the North Atlantic Drift. A shift in NAO phase from high to low |
| 54 |
causes more subtropical-origin waters to enter the SPG and Greenland's boundary current system. Moreover, since air-sea heat and buoyancy losses are positively correlated with |
causes more subtropical-origin waters to enter the SPG and Greenland's boundary current system. Moreover, since air-sea heat and buoyancy losses are positively correlated with |
| 55 |
the NAO, subtropical waters brought into the SPG are subject to less cooling during periods of negative NAO. Therefore, a switch from positive to negative NAO conditions is followed |
the NAO, subtropical waters brought into the SPG are subject to less cooling during periods of negative NAO. Therefore, a switch from positive to negative NAO conditions is followed |
| 56 |
by a warming of IW in the SPG due to an increase the lateral ocean heat flux convergence and a decrease of air-sea heat loss (Yashayaev and Loder, 2009). |
by a warming of IW in the SPG due to an increase of lateral ocean heat flux convergence and a decrease of air-sea heat loss (Yashayaev and Loder, 2009). |
| 57 |
|
|
| 58 |
From the late 1980s to the early 1990s, the NAO was mainly in a positive phase resulting in a cooler, fresher, and laterally expansive SPG with comparatively colder and fresher |
From the late 1980s to the early 1990s, the NAO was mainly in a positive phase resulting in a cooler, fresher, and laterally expansive SPG with comparatively colder and fresher |
| 59 |
IW in the SPG and the East/West Greenland Current (EGC/WGC). Following this period of sustained positive values, the NAO exhibited a dramatic reduction in the mid-1990s and |
IW in the SPG and the East/West Greenland Current (EGC/WGC). Following this period of sustained positive values, the NAO exhibited a dramatic reduction in the mid-1990s and |
| 72 |
\section{2.0 Model configuration and Methodology.} |
\section{2.0 Model configuration and Methodology.} |
| 73 |
|
|
| 74 |
The results described herein are based on a regional configuration of the Massachusetts Institute of Technology general circulation model (MITgcm; Marshall and others, 1997). |
The results described herein are based on a regional configuration of the Massachusetts Institute of Technology general circulation model (MITgcm; Marshall and others, 1997). |
| 75 |
The domain of integration includes the entire Arctic Ocean and parts of the North Pacific and North Atlantic (see Fig.~1 in Nguyen and others, 2011). Model grid spacing is |
The domain of integration includes the entire Arctic Ocean and parts of the North Pacific and North Atlantic (see Fig.\ 1 in Nguyen and others, 2011). Model grid spacing is |
| 76 |
4 km in the horizontal and ranges between 10 and 450 m over 50 levels in the vertical. The model employs the rescaled vertical coordinate z$^{*}$ of Adcroft and Campin (2004) and the partial-cell formulation of Adcroft and others (1997) . The ocean model is coupled to the dynamic and thermodynamic sea ice model described in Losch and others (2010) and employs the salt plume parameterization of |
4 km in the horizontal and ranges between 10 and 450 m over 50 levels in the vertical. The model employs the rescaled vertical coordinate z$^{*}$ of Adcroft and Campin (2004) and the partial-cell formulation of Adcroft and others (1997) . The ocean model is coupled to the dynamic and thermodynamic sea ice model described in Losch and others (2010) and employs the salt plume parameterization of |
| 77 |
Nguyen and others (2009). Ocean and sea ice model parameters are identical to the 18-km optimized solution called A1 in Nguyen and others (2011). Ocean initial and lateral open boundary conditions of temperature and salinity are derived from the World Ocean Atlas 2005 (WOA05; Boyer and others, 2006) while velocities on the open boundaries are derived from the global eddying ECCO2 state estimate of Menemenlis and others (2008). Air-sea fluxes are calculated with the bulk formulae of Large and Yeager (2008) and the Japanese 25-year ReAnalysis and the Japan Meteorological Agency Climate Data Assimilation System(JRA-25/JCDAS; Onogi and others, 2007). Bathymetry is derived from the International Bathymetric Chart of the Arctic Ocean (IBCAO) (Jakobsson and others, 2008). A preliminary |
Nguyen and others (2009). Ocean and sea ice model parameters are identical to the 18-km optimized solution called A1 in Nguyen and others (2011). Ocean initial and lateral open boundary conditions of temperature and salinity are derived from the World Ocean Atlas 2005 (WOA05; Boyer and others, 2006) while velocities on the open boundaries are derived from the global, eddying ECCO2 state estimate of Menemenlis and others (2008). Air-sea fluxes are calculated with the bulk formulae of Large and Yeager (2008) and the Japanese 25-year ReAnalysis and the Japan Meteorological Agency Climate Data Assimilation System (JRA-25/JCDAS; Onogi and others, 2007). Bathymetry is derived from the International Bathymetric Chart of the Arctic Ocean (IBCAO) (Jakobsson and others, 2008). A preliminary |
| 78 |
evaluation of the Arctic Ocean in the model is given in Nguyen and others (2012). |
evaluation of the Arctic Ocean in the model is given in Nguyen and others (2012). |
| 79 |
|
|
| 80 |
The realistic simulation of hydrographic variability and circulation dynamics in glacial fjords requires very high model horizontal resolution ($<$ 1 km), good bathymetric data, and, in some locations, representation of the effects of tidal forcing. Given the model resolution, the lack of a tidal submodel, and limited bathymetry knowledge, the model is analyzed near the mouths of the glacial fjords. Hydrographic changes at the fjord mouths may only be partially transmitted through the fjords to the glacier fronts. Most Greenland fjords are sill fjords (Buch, 2002; and Table 1), i.e. warm subsurface waters have to overcome topographic barriers to penetrate the glacial fjords and reach the glacier fronts. Once at the ice fronts, these ocean waters participate in a vigorous thermohaline circulation driven by subglacial water discharge at the glacier front, the buoyancy of freshwater at the |
The realistic simulation of hydrographic variability and circulation dynamics in glacial fjords requires very high model horizontal resolution ($<$ 1 km), good bathymetric data, and, in some locations, representation of the effects of tidal forcing. Given the model resolution, the lack of a tidal submodel, and limited bathymetry knowledge, the model is analyzed near the mouths of the glacial fjords. Hydrographic changes at the fjord mouths may only be partially transmitted through the fjords to the glacier fronts. Most Greenland fjords are sill fjords (Buch, 2002; and Table 1), i.e., warm subsurface waters have to overcome topographic barriers to penetrate the glacial fjords and reach the glacier fronts. Once at the ice fronts, these ocean waters participate in a vigorous convective circulation driven by subglacial water discharge at the glacier front, the buoyancy of freshwater at the |
| 81 |
front, and the pressure dependence of the melting point of seawater (Motyka and others, 2003; Xu and others, 2012). When subglacial flow is low or absent, the forced convection is |
front, and the pressure dependence of the melting point of seawater (Motyka and others, 2003; Xu and others, 2012). When subglacial flow is low or absent, the forced convection is |
| 82 |
strongly reduced, and vigorous ice melting ceases as observed on Columbia Glacier, Alaska (Walters and others, 1988). |
strongly reduced, and vigorous ice melting ceases as observed on Columbia Glacier, Alaska (Walters and others, 1988). |
| 83 |
|
|
| 85 |
\subsection{3.1 General trends.} |
\subsection{3.1 General trends.} |
| 86 |
|
|
| 87 |
Figure 1a shows the simulated ocean temperature at 250 m depth, time-averaged for the entire 1992--2009 period. The warmest, saltiest waters are found to the east of the Reykjanes |
Figure 1a shows the simulated ocean temperature at 250 m depth, time-averaged for the entire 1992--2009 period. The warmest, saltiest waters are found to the east of the Reykjanes |
| 88 |
ridge, subtropical-origin waters transported northward by the North Atlantic Current, with temperatures $ \geq+8^\circ$ C at this depth. These waters are transported west by |
Ridge. These are subtropical-origin waters transported northward by the North Atlantic Current, with temperatures $\geq 8^\circ$C at this depth. These waters are transported west by |
| 89 |
the Irminger Current (IC, Fig.~1b) towards Southeast Greenland and north towards Svalbard and Northeast Greenland by the Norwegian Atlantic and West Spitsburgen Currents. At the shelf |
the Irminger Current (IC, Fig.\ 1b) towards Southeast Greenland and north towards Svalbard and Northeast Greenland by the Norwegian Atlantic and West Spitsburgen Currents. At the shelf |
| 90 |
along Southeast Greenland they combine with the cold (1$^\circ$C), low salinity shelf waters of the EGC coming from the Arctic and Nordic Seas (Sutherland and Pickard, 2008) to |
along Southeast Greenland they combine with the cold (1$^\circ$C), low salinity shelf waters of the EGC coming from the Arctic and Nordic Seas (Sutherland and Pickard, 2008) to |
| 91 |
form a two-component current with cold fresh waters above the shelf and warm salty waters along the slope. The EGC rounds the southern tip of Greenland at Cape Farewell to become |
form a two-component current with cold fresh waters above the shelf and warm salty waters along the slope. The EGC rounds the southern tip of Greenland at Cape Farewell to become |
| 92 |
the northward-flowing WGC, with subsurface ocean temperatures 2--3$^\circ$C lower than the IC, due to air-sea heat losses and lateral mixing. IW on the WGC is traceable in Fig.~1 as |
the northward-flowing WGC, with subsurface ocean temperatures 2--3$^\circ$C lower than the IC, due to air-sea heat losses and lateral mixing. IW on the WGC is traceable in Fig.\ 1 as |
| 93 |
the warm and fast-moving water flowing northward along the slope at 250m. A portion of the WGC bifurcates west into the Labrador Sea and joins the Labrador Current (LC) to complete |
the warm and fast-moving water flowing northward along the slope at 250 m. A portion of the WGC bifurcates west into the Labrador Sea and joins the Labrador Current (LC) to complete |
| 94 |
the western branch of the SPG (Fig.~1b). The non-bifurcating northward-flowing branch of the WGC passes through eastern Davis Strait into Baffin Bay (Buch, 2002). In northern Baffin Bay, |
the western branch of the SPG (Fig.\ 1b). The non-bifurcating northward-flowing branch of the WGC passes through eastern Davis Strait into Baffin Bay (Buch, 2002). In northern Baffin Bay, |
| 95 |
the now significantly cooler IW on the WGC (1$^\circ$C) meets colder ($\leq 0^\circ$C), fresher southward-flowing Arctic currents from |
the now significantly cooler IW on the WGC (1$^\circ$C) meets colder ($\leq 0^\circ$C), fresher southward-flowing Arctic currents from |
| 96 |
Nares Strait, Jones and Lancaster Sound. Together, these waters flow southward along Baffin Island in the Baffin Island Current (BIC) through western Davis Strait to the LC. In Northeast Greenland, the subtropical-origin waters joining the EGC are much cooler (3.5--5$^\circ$C) than those waters joining farther south, a result of cooling during its northward transit. |
Nares Strait, and from Jones and Lancaster Sound. Together, these waters flow southward along Baffin Island in the Baffin Island Current (BIC) through western Davis Strait to the LC. In Northeast Greenland, the subtropical-origin waters joining the EGC are much cooler (3.5--5$^\circ$C) than those waters joining farther south, a result of cooling during its northward transit. |
| 97 |
|
|
| 98 |
The 4-km ECCO2 solution reveals major changes in subsurface ocean temperature around Greenland during the 1992--2009 time period (Fig.~1c and d). As the NAO ceased its sustained positive |
The 4-km ECCO2 solution reveals major changes in subsurface ocean temperature around Greenland during the 1992--2009 time period (Fig.\ 1c and d). As the NAO ceased its sustained positive |
| 99 |
phase, IW in the SPG warmed and propagated along the EGC/WGC, yielding positive subsurface temperature anomalies in Southeast, Southwest, and Northwest Greenland. The warming around North and Northeast Greenland took considerably longer, a result of the longer advective timescales associated with the propagation of subtropical-origin waters into the Greenland Sea and Arctic Ocean (Fig. 1c). During |
phase, IW in the SPG warmed and propagated along the EGC/WGC, yielding positive subsurface temperature anomalies in Southeast, Southwest, and Northwest Greenland. The warming around North and Northeast Greenland took considerably longer, a result of the longer advective timescales associated with the propagation of subtropical-origin waters into the Greenland Sea and Arctic Ocean (Fig.\ 1c). During |
| 100 |
the second half of the simulation period, the model indicates widespread warming in Baffin Bay and Greenland Sea and a cooling in the Eastern Irminger Sea and Southeast Greenland (Fig. 1d). |
the second half of the simulation period, the model indicates widespread warming in Baffin Bay and Greenland Sea and a cooling in the Eastern Irminger Sea and Southeast Greenland (Fig.\ 1d). |
| 101 |
|
|
| 102 |
\subsection{3.2 Comparison with {\it in situ} data} |
\subsection{3.2 Comparison with {\it in situ} data} |
| 103 |
|
|
| 104 |
We compare the 4-km ECCO2 solution with {\it in situ} observations in the central Labrador Sea (within 150 km of the AR7W line and in depths exceeding 3,250 m), the western Irminger Sea |
We compare the 4-km ECCO2 solution with {\it in situ} observations in the central Labrador Sea (within 150 km of the AR7W line and in depths exceeding 3,250 m), the western Irminger Sea |
| 105 |
(within 150 km of the AR7E line, in depths exceeding 2,500 m, and west of 36$^\circ$W), and in Eastern Baffin Bay (between 71-74$^\circ$N, east of 60$^\circ$W, and in waters shallower |
(within 150 km of the AR7E line, in depths exceeding 2,500 m, and west of 36$^\circ$W), and in Eastern Baffin Bay (between 71--74$^\circ$N, east of 60$^\circ$W, and in waters shallower |
| 106 |
than 550 m) (Fig.~2). Temperature data are drawn from CTDs, autonomous profiling floats, and expendable bathy-thermographs (XBT) compiled from the Hydrobase 2 of Curry (2001), |
than 550 m) (Fig.\ 2). Temperature data are drawn from CTDs, autonomous profiling floats, and expendable bathy-thermographs (XBT) compiled from the Hydrobase 2 of Curry (2001), the |
| 107 |
Global Temperature and Salinity Profile Program from the National Oceanographic Data Center Operational Ocenography Group (NODC 2006) and the ICES Oceanographic Database |
Global Temperature and Salinity Profile Program of the National Oceanographic Data Center Operational Ocenography Group (NODC 2006), and the ICES Oceanographic Database |
| 108 |
and Services (ICES 2012). |
and Services (ICES 2012). |
| 109 |
|
|
| 110 |
The 4-km ECCO2 simulation is initialized from the WOA05 climatology, a climatology which, by coincidence, includes several important observed features of the SPG in 1992 including |
The 4-km ECCO2 simulation is initialized from the WOA05, a temperature and salinity atlas, which, by coincidence, includes several important observed features of the SPG in 1992 including |
| 111 |
a relatively cool and weakly-stratified interior. Compared to observations in the Labrador and Irminger Seas between 1992 and 1996, the climatology has an approximately +0.4$^\circ$C |
a relatively cool and weakly-stratified interior. Compared to observations in the Labrador and Irminger Seas between 1992 and 1996, the WOA05 has approximately +0.4$^\circ$C |
| 112 |
bias. This constant bias has been removed from the model results in Figure 2 and 3 in order to focus the discussion on temporal trends. |
bias. This constant bias has been removed from the model results in Figs.\ 2 and 3 in order to focus the discussion on temporal trends. |
| 113 |
|
|
| 114 |
Waters within the SPG have significantly warmed since the mid-1990s owing to a shift to generally milder wintertime atmospheric conditions. With reduced wintertime air-sea heat losses, |
Waters within the SPG have significantly warmed since the mid-1990s owing to a shift to generally milder wintertime atmospheric conditions. With reduced wintertime air-sea heat losses, |
| 115 |
net lateral advective heat flux convergence into the subpolar gyre has dominated over atmospheric heat loss. The model closely reproduces the magnitude and timing of the observed interior warming of the Labrador and Irminger Seas: about +1.0$^\circ$C in the upper 500 m between 1992 and 2004 and |
net lateral advective heat flux convergence into the subpolar gyre has dominated over atmospheric heat loss. The model closely reproduces the magnitude and timing of the observed interior warming of the Labrador and Irminger Seas: about +1.0$^\circ$C in the upper 500 m between 1992 and 2004 and |
| 116 |
+0.6$^\circ$C between 500 and 2,000 m. In the Labrador Sea, temperatures in the upper 500 m cease their dramatic warming by 2004 and thereafter exhibit |
+0.6$^\circ$C between 500 and 2,000 m. In the Labrador Sea, temperatures in the upper 500 m cease their dramatic warming by 2004 and thereafter exhibit |
| 117 |
inter-annual variability consistent with known atmospheric variability (e.g., the cooling/deep convection event of 2008 (Vage, 2011). |
inter-annual variability consistent with known atmospheric variability (e.g., the cooling/deep convection event of 2008; Vage, 2011). |
| 118 |
|
|
| 119 |
We expect the simulated SPG warming to be limited for several reasons. Lohmann and others (2009) showed that the response of the SPG to a shift from NAO+ to NAO$-$ conditions is |
We expect the simulated SPG warming to be limited for several reasons. Lohmann and others (2009) showed that the response of the SPG to a shift from NAO+ to NAO$-$ conditions is |
| 120 |
sensitive to the amount of preconditioning by the atmosphere. The model initial conditions are identical to the WOA05 and are, therefore, not preconditioned by the NAO+ forcing which |
sensitive to the amount of preconditioning by the atmosphere. The model initial conditions are identical to the WOA05 and are, therefore, not preconditioned by the NAO+ forcing, which |
| 121 |
began in the late 1980s. In addition, because the lateral ocean open boundaries are taken from WOA05, the waters feeding the SPG do not exhibit realistic inter-annual |
began in the late 1980s. In addition, because the lateral ocean open boundaries are taken from WOA05, the waters feeding the SPG do not exhibit realistic inter-annual |
| 122 |
hydrographic variability. Finally, model-data differences include errors in the JRA-25/JCDAS surface boundary conditions and inaccuracies in the model subgrid-scale |
hydrographic variability. Finally, model-data differences include errors in the JRA-25/JCDAS surface boundary conditions and inaccuracies in the model subgrid-scale |
| 123 |
parameterizations. |
parameterizations. |
| 124 |
|
|
| 125 |
Comprehensive model-data comparison for the Eastern Baffin Bay region is considerably more difficult than the SPG owing to the paucity of {\it in situ} observations over the simulation period, |
Comprehensive model-data comparison for the Eastern Baffin Bay region is considerably more difficult than the SPG owing to the paucity of {\it in situ} observations over the simulation period, |
| 126 |
especially during the first four years where no measurements are available. Assuming that the ocean state in 1992 is similar to measurements taken in 1988 and 1990, the data indicate |
especially during the first four years where no measurements are available. Assuming that the ocean state in 1992 is similar to measurements taken in 1988 and 1990, the data indicate |
| 127 |
a warming of +1.0$^\circ$C between 100 and 300 m between 1992 and 1999. At these depths, the model is initially about 1.0$^\circ$C cooler than observations -- possibly an artifact of the |
a warming of +1.0$^\circ$C between 100 and 300 m between 1992 and 1999. At these depths, the model is initially about 1.0$^\circ$C cooler than observations --- possibly an artifact of the |
| 128 |
sparse data used to generate the climatology. However, the model warms to temperatures comparable to initial conditions by 1998 and then to contemporaneous observations by 1999-2000. |
sparse data used to generate the WOA05. However, the model warms to temperatures comparable to initial conditions by 1998 and then to contemporaneous observations by 1999-2000. |
| 129 |
A dip in 2005 temperatures is reproduced, as well as the subsequent +0.5$^\circ$C warming. Simulated temperatures in this region for the 2000s are in broad agreement with |
A dip in 2005 temperatures is reproduced, as well as the subsequent +0.5$^\circ$C warming. Simulated temperatures in this region for the 2000's are in broad agreement with |
| 130 |
Narwhal-based observations reported by Laidre and others (2010) who found maximum wintertime temperatures up to 3.4$^\circ$C at 350 m in the same region. |
Narwhal-based observations reported by Laidre and others (2010) who found maximum wintertime temperatures up to 3.4$^\circ$C at 350 m in the same region. |
| 131 |
|
|
| 132 |
In terms of total temperature change, the model exhibits an extra degree of warming in the Eastern Baffin Bay region than observed. Without additional experiments it is impossible to determine how much of the warming is due to a realistic model response to the specified atmospheric forcing versus the model evolving away from imperfect initial conditions versus systematic model errors. It also must be noted that the model analyses use all grid points and times whereas the |
In terms of total temperature change, the model exhibits an extra degree of warming in the Eastern Baffin Bay region than observed. Without additional experiments it is impossible to determine how much of the warming is due to a realistic model response to the specified atmospheric forcing as opposed to the model evolving away from imperfect initial conditions or to systematic model errors. It also must be noted that the model analyses use all grid points and times whereas the |
| 133 |
observation analyses rely on temporally and spatially sparse measurements. To illustrate, the impact of sample density on the observation |
observation analyses rely on temporally and spatially sparse measurements. To illustrate, the impact of sample density on the observation |
| 134 |
analyses can be seen by comparing the temperature reconstructions before and after the widespread arrival of ARGO floats in 2002. |
analyses can be seen by comparing the temperature reconstructions before and after the widespread arrival of ARGO floats in 2002. |
| 135 |
|
|
| 136 |
\subsection{3.3 Modeled regional changes} |
\subsection{3.3 Modeled regional changes} |
| 137 |
|
|
| 138 |
We examine changes in subsurface temperature at 7 key locations, spanning different oceanic regimes (Fig.~3). |
We examine changes in subsurface temperature at 7 key locations, spanning different oceanic regimes (Fig.\ 3). |
| 139 |
The survey starts at Kangerdlugssuaq Glacier on the East Coast, closest to the source of IW, and continues clockwise around Greenland. We analyze |
The survey starts at Kangerdlugssuaq Glacier on the East Coast, closest to the source of IW, and continues clockwise around Greenland. We analyze |
| 140 |
both off-the-shelf (triangles in Fig.~1a) and on-the-shelf (diamonds) simulated subsurface ocean temperature data, averaged over one-year periods and over the range of depths indicated |
both off-the-shelf (triangles in Fig.\ 1a) and on-the-shelf (diamonds) simulated subsurface ocean temperature data, averaged over one-year periods and over the range of depths indicated |
| 141 |
in Table~\ref{table:locations}. Anomalies in subsurface temperature are calculated in reference to the average temperature for the entire period. The comparison of off-the-shelf |
in Table~\ref{table:locations}. Anomalies in subsurface temperature are calculated in reference to the average temperature for the entire period. The comparison of off-the-shelf |
| 142 |
versus on-the-shelf temperature documents whether changes in ocean temperature are transmitted across the shelf break. Off-the-shelf locations are selected at the edge of the |
versus on-the-shelf temperature documents whether changes in ocean temperature are transmitted across the shelf break. Off-the-shelf locations are selected at the edge of the |
| 143 |
continental shelf, near major troughs in the seafloor; on-the-shelf locations are selected in front of major glacial fjords, within troughs. Troughs are important because they provide |
continental shelf, near major troughs in the seafloor; on-the-shelf locations are selected in front of major glacial fjords, within troughs. Troughs are important because they provide |
| 144 |
a natural pathway for subsurface warm waters to intrude onto the continental shelf and reach the glacial fjords. |
a natural pathway for subsurface warm waters to intrude onto the continental shelf and reach the glacial fjords. |
| 145 |
|
|
| 146 |
At Ko (Fig.~1a), the initial ocean temperatures off the shelf have the warmest IW of our locations, +5.8$^\circ$C. Ko is far offshore from Ks due to a broad continental shelf in that area. |
At off-the-shelf location K$_O$ (Fig.\ 1a), the initial ocean temperatures have the warmest (5.8$^\circ$C) IW of the seven selected locations. K$_O$ is far offshore from K$_S$ due to a broad continental shelf in that area. |
| 147 |
In 1994--2004, the modeled subsurface ocean temperature increased by +1.3$^\circ$ at Ko; and did not significantly change thereafter. On the shelf, the temperature at Ks is initially 3.1$^\circ$C |
In 1994--2004, the modeled subsurface ocean temperature increased by +1.3$^\circ$ at K$_O$; and did not significantly change thereafter. On the shelf, the temperature at K$_S$ is initially 3.1$^\circ$C |
| 148 |
colder than off the shelf (+2.7$^\circ$C at Ks vs +5.8$^\circ$C at Ko); and the warming is +1.2$^\circ$C in 1994--2004, with little warming in later years. At SEo in the southeast, ocean temperature |
colder than off the shelf (2.7$^\circ$C at K$_S$ vs 5.8$^\circ$C at K$_O$); and the warming is +1.2$^\circ$C in 1994--2004, with little warming in later years. At SE$_O$ in the southeast, ocean temperature |
| 149 |
changes are synchronous with Ko with a warming of +1.2$^\circ$C in 1994--2004. In contrast with Ko and Ks, both on- and off-the-shelf areas decline by 0.5$^\circ$C after |
changes are synchronous with K$_O$ with a warming of +1.2$^\circ$C in 1994--2004. In contrast with K$_O$ and K$_S$, both on- and off-the-shelf areas decline by 0.5$^\circ$C after |
| 150 |
2005, yielding an overall warming for the entire period of about +1$^\circ$C. |
2005, yielding an overall warming for the entire period of about +1$^\circ$C. |
| 151 |
|
|
| 152 |
On the west coast at No, simulated subsurface temperature changes are +1.8$^\circ$C in 1994--2004 and -0.6$^\circ$C after 2006. At Ns, both the warming (+2$^\circ$C) and cooling |
On the west coast at N$_O$, simulated subsurface temperature changes are +1.8$^\circ$C in 1994--2004 and $-0.6^\circ$C after 2006. At N$_S$, both the warming (+2$^\circ$C) and cooling |
| 153 |
(-1.0$^\circ$C) are larger than at No. Larger temperature changes are modeled near the mouth of Disko Bay with +2.5$^\circ$C in 1993--2003 at Jo. After 2004, Js continues to warm by |
($-1.0^\circ$C) are larger than at N$_O$. Larger temperature changes are modeled near the mouth of Disko Bay with +2.5$^\circ$C in 1993--2003 at J$_O$. After 2004, J$_S$ continues to warm by |
| 154 |
another +0.5$^\circ$C, but not Jo. Ocean waters at Jo are initially 4$^\circ$C colder than at Ko. |
another +0.5$^\circ$C, but not J$_O$. Ocean waters at J$_O$ are initially 4$^\circ$C colder than at K$_O$. |
| 155 |
|
|
| 156 |
Farther north, in Melville Bay, modeled ocean waters at Mo are 2.6$^\circ$C colder than in Disko Bay at Jo (+0.4$^\circ$C versus +3$^\circ$C for the entire period) and warmed by +3$^\circ$C |
Farther north, in Melville Bay, modeled ocean waters at M$_O$ are 2.6$^\circ$C colder than in Disko Bay at J$_O$ (0.4$^\circ$C versus 3$^\circ$C for the entire period) and warmed by +3$^\circ$C |
| 157 |
in 1994-2009 for both the off- and on-shelf locations. The most significant warming takes place after 1997 and after 2004. This delayed warming compared to the south is expected from the |
in 1994--2009 for both the off- and on-shelf locations. The most significant warming takes place after 1997 and after 2004. This delayed warming compared to the south is expected from the |
| 158 |
northward spreading of warm waters. In North and Northeast Greenland, where subsurface temperature anomalies are not directly linked to the SPG via the WGC pathway, warming is delayed until |
northward spreading of warm waters. In North and Northeast Greenland, where subsurface temperature anomalies are not directly linked to the SPG via the WGC pathway, warming is delayed until |
| 159 |
after 2004. The modeled change at 79Ns (+1$^\circ$C) is less than at 79No (+1.5$^\circ$C), suggesting that only a fraction of the available ocean heat is transmitted to up the shelf at this location. |
after 2004. The modeled change at 79N$_S$ (+1$^\circ$C) is less than at 79N$_O$ (+1.5$^\circ$C), suggesting that only a fraction of the available ocean heat is transmitted up to the shelf at this location. |
| 160 |
|
|
| 161 |
\subsection{3.4 Modeled regional trends versus observations} |
\subsection{3.4 Modeled regional trends versus observations} |
| 162 |
|
|
| 163 |
The +1.6$^\circ$C modeled warming at Ks between 1995 and 1998 is consistent with the +1.8$^\circ$C warming reported by Christoffersen and others (2011). On the southwest coast at Ns and |
The +1.6$^\circ$C modeled warming at K$_S$ between 1995 and 1998 is consistent with the +1.8$^\circ$C warming reported by Christoffersen and others (2011). On the southwest coast at N$_S$ and |
| 164 |
No, the +1.5 to +2$^\circ$C modeled warming for 1995--1999 is consistent with the observations reported by Myers and others (2007), followed by a cooling in 2007--2009. In Disko Bay, Holland |
N$_O$, the +1.5 to +2$^\circ$C modeled warming for 1995--1999 is consistent with the observations reported by Myers and others (2007), followed by a cooling in 2007--2009. In Disko Bay, Holland |
| 165 |
and others (2008) reported an increase of 1.2$^\circ$C in 1991--1996 to almost 3$^\circ$C in 1997--1999 from fish trawl data depth-averaged between 150 and 600~m in their Region 2 (Wieland |
and others (2008) reported an increase of +1.2$^\circ$C in 1991--1996 to almost +3$^\circ$C in 1997--1999 from fish trawl data, depth-averaged between 150 and 600~m in their Region 2 (Wieland |
| 166 |
and Kanneworff, 2002). Over the entire survey area, they report an increase from +1.7$^\circ$C to +3.5$^\circ$C until year 2002. Over that same period, the model indicates a +2$^\circ$C warming, |
and Kanneworff, 2002). Over the entire survey area, they report an increase from +1.7$^\circ$C to +3.5$^\circ$C until year 2002. Over that same period, the model indicates a +2$^\circ$C warming, |
| 167 |
which agrees with the fish trawl data, and a continuous warming after 2002. In terms of timing, the modeled change in ocean temperature at Js is abrupt in 1995--1998 and |
which agrees with the fish trawl data, and a continuous warming after 2002. In terms of timing, the modeled change in ocean temperature at J$_S$ is abrupt in 1995--1998 and |
| 168 |
moderate in 1998--2002, which is again consistent with fish trawl data. |
moderate in 1998--2002, which is again consistent with fish trawl data. |
| 169 |
|
|
| 170 |
Few observations exist in Eastern Baffin Bay near Ms and Mo to evaluate the realism of the simulated trend. As discussed in Section 3.2, existing data suggests that the model started 1$^\circ$C too cold and the modeled warming |
Few observations exist in Eastern Baffin Bay near M$_S$ and M$_O$ to evaluate the realism of the simulated trend. As discussed in Section 3.2, existing data suggest that the model started 1$^\circ$C too cold and the modeled warming |
| 171 |
is also 1$^\circ$C too large. At Ps, Johnson and others (2010) report only 0.25$^\circ$C warming from 2003 to 2009 versus less than 0.5$^\circ$C in the model over that time period. We conclude that |
is also 1$^\circ$C too large. At P$_S$, Johnson and others (2010) report only +0.25$^\circ$C warming from 2003 to 2009 versus approximately +0.4$^\circ$C in the model over that time period. We conclude that |
| 172 |
the model results in the north tend to overestimate the warming compared to observations. |
the model results in the north tend to overestimate the warming compared to observations. |
| 173 |
|
|
| 174 |
\subsection{3.5 Potential for ocean heat to intrude glacial fjords} |
\subsection{3.5 Potential for ocean heat to intrude glacial fjords} |
| 175 |
|
|
| 176 |
Our analysis suggests that over the sites considered, changes in ocean temperature off the shelf are transmitted rapidly on the shelf. Whether the on-the-shelf changes reach the |
Our analysis suggests that over the sites considered, changes in ocean temperature off the shelf are transmitted rapidly on the shelf. Whether the on-the-shelf changes reach the |
| 177 |
glacier fronts depends on winds, air-ocean heat exchange within the fjords and especially seafloor topography, i.e. the presence of sills that may block the migration of warm, |
glacier fronts depends on winds, air-ocean heat exchange within the fjords, and, most importantly, seafloor topography, i.e., the presence of sills that may block the migration of warm, |
| 178 |
subsurface waters. Most sill depths are not well known (Buch, 2002). At Kangerdlugssuaq and Helheim (Ks and SEs), the main sill depth of 550m should let warm subsurface waters penetrate the glacial fjord |
subsurface waters. Most sill depths are not well known (Buch, 2002). At Kangerdlugssuaq and Helheim (K$_S$ and SE$_S$), the main sill depth of 550 m should let warm subsurface waters penetrate the glacial fjord |
| 179 |
(Table 1). Sill depths farther south are unknown (Buch, 2002). At Ns, the main sill depth of 80 m should block warm water inflows. At JKS, the 350-m deep sill is not sufficient to block warm waters from |
(Table 1). Sill depths farther south are unknown (Buch, 2002). At N$_S$, the main sill depth of 80 m should block warm water inflow. At JKS, the 350-m deep sill is not sufficient to block warm waters from |
| 180 |
intruding the fjord (Holland and others, 2008), but at Torssukataq the sill depth is only 285 m. In northwest Greenland, there is no bathymetry data within 100 km of the coastline in |
intruding the fjord (Holland and others, 2008), but at Torssukataq the sill depth is only 285 m. In northwest Greenland, there is no bathymetry data within 100 km of the coastline in |
| 181 |
the IBCAO data base. At Ps, the 380-m depth sill should not not block warm waters, but a shallower sill exists inside the fjord. At 79Ns, the sill depth is |
the IBCAO data base. At P$_S$, the 380-m depth sill should not not block warm waters, but a shallower sill exists inside the fjord. At 79N$_S$, the sill depth is |
| 182 |
20 to 200m, so warm waters are blocked off. |
20 to 200 m, so warm waters are blocked off. |
| 183 |
|
|
| 184 |
\subsection{3.6 Comparison of enhanced melt rates with glacier-front retreat and acceleration} |
\subsection{3.6 Comparison of enhanced melt rates with glacier-front retreat and acceleration} |
| 185 |
|
|
| 186 |
Model simulations suggest that the subaqueous melt rate of a glacier calving face increases linearly with thermal forcing defined as the difference between the water temperature and |
Model simulations suggest that the subaqueous melt rate of a glacier calving face increases linearly with thermal forcing, defined as the difference between the water temperature and |
| 187 |
the {\em in situ} freezing point of seawater (Xu et al., 2012). We use this linear relationship herein to calculate the percentage increase in subaqueous melt rate resulting from an increase in |
the {\em in situ} freezing point of seawater (Xu et al., 2012). We use this linear relationship herein to calculate the percentage increase in subaqueous melt rate resulting from an increase in |
| 188 |
ocean temperature (Table 1). We use a constant freezing point of seawater of -2.08$^\circ$C for a depth of 250 m and a salinity of 34.5 psu. |
ocean temperature (Table 1). We use a constant freezing point of seawater of $-2.08^\circ$C for a depth of 250 m and a salinity of 34.5 psu. |
| 189 |
|
|
| 190 |
At Ks, Kangerdlugssuaq Gletscher doubled its speed in 2004--2005, retreated 6 km and re-advanced by 2 km in 2007--2009 with a 50\% reduction in speed (Howat and others, 2007). In the model, |
At K$_S$, Kangerdlugssuaq Gletscher doubled its speed in 2004--2005, retreated 6 km, and then re-advanced by 2 km in 2007--2009 with a 50\% reduction in speed (Howat and others, 2007). In the model, |
| 191 |
warm waters intruded at Ks after 1996 until 2004, followed by a slight cooling. The modeled temperatures translate into a 24\% increase in melt rate over the entire time period and 36\% |
warm waters intruded at K$_S$ from 1996 to 2004, followed by a slight cooling. The modeled temperatures translate into a 24\% increase in melt rate over the entire time period and 36\% |
| 192 |
between 1992 and 2004 (Table 1). |
between 1992 and 2004 (Table 1). |
| 193 |
At Helheim, the glacier accelerated in 2002--2003 and doubled its speed by 2005; the ice front retreated by 7 km before re-advancing by 3 km in 2005--2006 and slowing down by 25\% |
At Helheim, the glacier accelerated in 2002--2003 and doubled its speed by 2005; the ice front retreated by 7 km before re-advancing by 3 km in 2005--2006 and slowing down by 25\% |
| 194 |
(Howat and others, 2007). The modeled changes in temperature at SEs suggests a 14\% increase in subaqueous melt for 1993-2009 and 21\% for 1993-2004. The 1993-2004 increase in melt |
(Howat and others, 2007). The modeled changes in temperature at SE$_S$ suggests a 14\% increase in subaqueous melt for 1993--2009 and 21\% for 1993--2004. The 1993--2004 increase in melt |
| 195 |
rate may have been sufficient to retreat the glacier front behind a shallow bathymetric feature (Joughin and others, 2008) and trigger speed up. The timing of the retreat and advance coincides |
rate may have been sufficient to retreat the glacier front behind a shallow bathymetric feature (Joughin and others, 2008) and trigger speed up. The timing of the retreat and advance coincides |
| 196 |
with the warming and subsequent cooling of ocean waters at SEs after 2004. A similar time evolution is found in Southeast Greenland (Murray and others, 2010). |
with the warming and subsequent cooling of ocean waters at SE$_S$ after 2004. A similar time evolution is found in Southeast Greenland (Murray and others, 2010). |
| 197 |
|
|
| 198 |
Near Nuuk, glacier changes at Kangiata Nunata have been few despite the presence of warm waters on the continental shelf, probably because shallow sills block the entrance |
Near Nuuk, glacier changes at Kangiata Nunata have been few despite the presence of warm waters on the continental shelf, probably because shallow sills block the entrance |
| 199 |
of warm subsurface waters. In Disko Bay, the ocean warming translate into a 68\% increase in melt rate, the largest in Greenland. Farther north, in Torssukataq fjord, glacier changes |
of warm subsurface waters. In Disko Bay, the ocean warming translates into a 68\% increase in melt rate, the largest in Greenland. Farther north, in Torssukataq fjord, glacier changes |
| 200 |
have been less significant, which may be due to the presence of a shallower sill. |
have been less significant, which may be due to the presence of a shallower sill. |
| 201 |
|
|
| 202 |
In Northwest Greenland, glacier acceleration along the coast has been sporadic (e.g., Moon and Joughin, 2007), but the glaciers have consistently lost mass since the 1990s and the mass |
In Northwest Greenland, glacier acceleration along the coast has been sporadic (e.g., Moon and Joughin, 2007), but the glaciers have consistently lost mass since the 1990s and the mass |
| 204 |
of +65\%, which is comparable to the record increase in Disko Bay. |
of +65\%, which is comparable to the record increase in Disko Bay. |
| 205 |
|
|
| 206 |
At Petermann Fjord, no significant glaciological changes occurred until a major calving event took place in 2010 (Johnson and others, 2011). Further observations and model |
At Petermann Fjord, no significant glaciological changes occurred until a major calving event took place in 2010 (Johnson and others, 2011). Further observations and model |
| 207 |
evaluation are needed to determine whether ocean warming had an impact on the stability of the floating ice tongue. In the northeast, the 79north glacier has been stable since the 1990s, which |
evaluation are needed to determine whether ocean warming had an impact on the stability of the floating ice tongue. In the northeast, the 79north glacier has been stable since the 1990's, which |
| 208 |
is consistent with the presence of shallow sills at the mouth of the fjord. |
is consistent with the presence of shallow sills at the mouth of the fjord. |
| 209 |
|
|
| 210 |
\section{4.0 Discussion.} |
\section{4.0 Discussion.} |
| 211 |
|
|
| 212 |
The dramatic change of atmospheric conditions in the North Atlantic in the mid-1990s is widely understood to have instigated a weakening of the SPG, and a consequent redistribution and warming of subtropical-origin waters in the SPG. Upon entering the subsurface shelfbreak component of the EGC, the warm anomaly propagated north above the West Greenland Shelf on the WGC to Eastern Baffin Bay. The 4-km Arctic Ocean ECCO2 simulation captures the warming around Greenland that is expected from a weakening SPG. Simulated temperatures are consistently warmer than observations in the interior SPG by about +0.4$^\circ$C -- probably due to the WOA05 climatology for |
The dramatic change of atmospheric conditions in the North Atlantic in the mid-1990's is widely understood to have instigated a weakening of the SPG, and a consequent redistribution and warming of subtropical-origin waters in the SPG. Upon entering the subsurface shelfbreak component of the EGC, the warm anomaly propagated north above the West Greenland Shelf on the WGC to Eastern Baffin Bay. The 4-km Arctic Ocean ECCO2 simulation captures the warming around Greenland that is expected from a weaken SPG. Simulated temperatures, however, are consistently warmer than observations in the interior SPG by about +0.4$^\circ$C --- probably due to a bias in the WOA05, which was used for |
| 213 |
initial conditions. Despite starting from a warmer state, the model reproduces the magnitude and timing of the successive warming of the SPG interior quite well following the switch from |
initial conditions. Despite starting from a warmer state, the model reproduces the magnitude and timing of the successive warming of the SPG interior quite well, following the switch from |
| 214 |
NAO+ to NAO- conditions. In Eastern Baffin Bay, the magnitude of simulated warming is much greater than observed. However, the climatology from which the model |
NAO+ to NAO$-$ conditions. In Eastern Baffin Bay, the magnitude of simulated warming is much greater than observed. However, the WOA05, from which the model |
| 215 |
was initialized appears to be too cold in that area than the sparse observations from the late 1980s and early 1990s indicate. Ultimately, the simulated Eastern Baffin Bay warming |
was initialized, appears to be colder in that region than the sparse observations from the late 1980's and early 1990's indicate. Ultimately, the simulated Eastern Baffin Bay warming |
| 216 |
brings model temperatures closer to more recent observations. |
brings model temperatures closer to more recent observations. |
| 217 |
|
|
| 218 |
Despite its limitations, the model is able to reproduce the observed patterns of warming around Southeast and Southwest Greenland and subsequent cooling in the Southeast Greenland when forced by JRA-25/JCDAS surface boundary conditions. The model indicates widespread ocean warming, including in Northwest Greenland after 2005. |
Despite its limitations, the model is able to reproduce the observed patterns of warming around Southeast and Southwest Greenland and subsequent cooling in the Southeast Greenland when forced by JRA-25/JCDAS surface boundary conditions. The model indicates widespread ocean warming, including in Northwest Greenland after 2005. |
| 221 |
Jenkins (2011) and Xu and others (2012) find a linear dependence on thermal forcing and a 1/3 power law dependence on the flux of subglacial runoff. Runoff has roughly doubled in Greenland in |
Jenkins (2011) and Xu and others (2012) find a linear dependence on thermal forcing and a 1/3 power law dependence on the flux of subglacial runoff. Runoff has roughly doubled in Greenland in |
| 222 |
1996--2006 compared to the colder 1987--1996 period (Ettema and others, 2009). A doubling in subglacial runoff should increase subaqueous melt by +25\% according to the model simulations. |
1996--2006 compared to the colder 1987--1996 period (Ettema and others, 2009). A doubling in subglacial runoff should increase subaqueous melt by +25\% according to the model simulations. |
| 223 |
If we combine this result with the increases in melt rate discussed in Section 3.6 based on changes in ocean thermal forcing (Table 1), we obtain a total potential increase in |
If we combine this result with the increases in melt rate discussed in Section 3.6 based on changes in ocean thermal forcing (Table 1), we obtain a total potential increase in |
| 224 |
subaqueous melt rate ranging from 40\% at SEs to 90\% at Js and Ms if subsurface warm waters were transmitted to the glacier fronts. |
subaqueous melt rate ranging from 40\% at SE$_S$ to 90\% at J$_S$ and M$_S$, if subsurface warm waters were transmitted to the glacier fronts. |
| 225 |
|
|
| 226 |
Enhanced subaqueous melting of the glacier fronts will undercut the glacier faces, increase calving and retreat the glacier fronts. Ice-front retreat will in turn reduce the buttressing force |
Enhanced subaqueous melting of the glacier fronts will undercut the glacier faces, increase calving and retreat the glacier fronts. Ice-front retreat will in turn reduce the buttressing force |
| 227 |
on the glaciers and entrain speed up (Thomas and others, 2004). To investigate in detail whether the calculated melt rates justify the observed glacier acceleration is an effort |
on the glaciers and engender speed up (Thomas and others, 2004). To investigate in detail whether the calculated melt rates justify the observed glacier acceleration is an effort |
| 228 |
well beyond the scope of this paper. Our analysis however indicates that the spreading of warm waters around Greenland must have significantly increased the glacier subaqueous melt rates in the |
well beyond the scope of this paper. Our analysis however indicates that the spreading of warm waters around Greenland must have significantly increased the glacier subaqueous melt rates in the |
| 229 |
frontal regions. |
frontal regions. |
| 230 |
|
|
| 231 |
\section{5.0 Conclusions.} |
\section{5.0 Conclusions.} |
| 232 |
|
|
| 233 |
Our examination of subsurface ocean temperature estimates for the 1992--2009 time period in the 4-km ECCO2 solution shows widespread warming of the coastal waters around Greenland, not only in the southeast and the southwest, but also in the northwest. Despite model uncertainties, the spatial and temporal pattern of these oceanic changes is a prominent feature |
Our examination of subsurface ocean temperature estimates for the 1992--2009 time period in the 4-km ECCO2 solution shows widespread warming of the coastal waters around Greenland, not only in the southeast and the southwest, but also in the northwest. Despite model uncertainties, the spatial and temporal pattern of these oceanic changes is a prominent feature |
| 234 |
of the model solution, which is consistent with available, albeit sparse, hydrographic data. These results reported here and in our companion study (Xu and others, 2012) support the hypothesis |
of the model solution, which is consistent with available, albeit sparse, hydrographic data. The results reported here and in a companion study (Xu and others, 2012) support the hypothesis |
| 235 |
that oceanic changes around Greenland have played a major role in the evolution of its glaciers, and in turn the entire ice sheet mass balance. Further progress in investigating the detailed |
that oceanic changes around Greenland have played a major role in the evolution of its glaciers and, in turn, the entire ice sheet mass balance. Further progress in investigating the detailed |
| 236 |
relationship between subsurface ocean conditions and glacier speed will require major advances in ocean modeling, bathymetry mapping, ice flow modeling, modeling of ice-ocean |
relationship between subsurface ocean conditions and glacier speed will require major advances in ocean modeling, bathymetry mapping, ice flow modeling, modeling of ice-ocean |
| 237 |
interactions and oceanographic data collection in glacial fjords. Our results suggest that high-resolution ocean models will soon become a useful tool of analysis for the glaciological community to address this issue in a quantitative fashion. |
interactions, and oceanographic data collection in glacial fjords. Our results suggest that high-resolution ocean models will soon become a useful tool of analysis for the glaciological community to address this issue in a quantitative fashion. |
| 238 |
|
|
| 239 |
Acknowledgments. This work was performed under contracts with the National Aeronautics and Space Administration's Cryospheric Science Program and Modeling Analysis and Prediction |
Acknowledgments. This work was performed under contracts with the National Aeronautics and Space Administration's Cryospheric Science Program and Modeling Analysis and Prediction |
| 240 |
Program. We thank three anonymous reviewers and the guest Editor for their constructive comments. |
Program. We thank three anonymous reviewers and the guest Editor for their constructive comments. |
| 368 |
\begin{tabular}{l c c c c c c c} \hline |
\begin{tabular}{l c c c c c c c} \hline |
| 369 |
Glacier & Main sill & Fjord max & GL & Region & Average T 92-94* & $\delta$T & Calculated $\delta$B \\ |
Glacier & Main sill & Fjord max & GL & Region & Average T 92-94* & $\delta$T & Calculated $\delta$B \\ |
| 370 |
& (m) & (m) & (m) & & $^\circ$C & $^\circ$C & \% \\ \hline |
& (m) & (m) & (m) & & $^\circ$C & $^\circ$C & \% \\ \hline |
| 371 |
Kangerdlugssuaq$^{1}$ & 500 & 870 & NA & Ks & 2.1 & +1.0 & 24 \\ |
Kangerdlugssuaq$^{1}$ & 500 & 870 & NA & K$_S$ & 2.1 & +1.0 & 24 \\ |
| 372 |
Helheim$^{2}$ & 550 & 920 & 550 & SEs & 5.1 & +1.0 & 14 \\ |
Helheim$^{2}$ & 550 & 920 & 550 & SE$_S$ & 5.1 & +1.0 & 14 \\ |
| 373 |
Kangiata Nunata$^{3}$ & 80 & 600 & NA & Ns & 3.6 & +1.0 & 18 \\ |
Kangiata Nunata$^{3}$ & 80 & 600 & NA & N$_S$ & 3.6 & +1.0 & 18 \\ |
| 374 |
Jakobshavn$^{4}$ & 350 & 800 & 600 & Js & 1.6 & +2.5 & 68 \\ |
Jakobshavn$^{4}$ & 350 & 800 & 600 & J$_S$ & 1.6 & +2.5 & 68 \\ |
| 375 |
Torssukataq$^{5}$ & 285 & 700 & 450 & Js & 1.6 & +2.0 & 54 \\ |
Torssukataq$^{5}$ & 285 & 700 & 450 & J$_S$ & 1.6 & +2.0 & 54 \\ |
| 376 |
Store$^{6}$ & NA & 950 & 550 & Js & 1.6 & +2.0 & 54 \\ |
Store$^{6}$ & NA & 950 & 550 & J$_S$ & 1.6 & +2.0 & 54 \\ |
| 377 |
King Oscar$^{7}$ & NA & 900 & NA & Ms & 1.0 & +2.0 & 65 \\ |
King Oscar$^{7}$ & NA & 900 & NA & M$_S$ & 1.0 & +2.0 & 65 \\ |
| 378 |
Petermann$^{8}$ & 380 & 900 & 550 & Ps & -0.25 & +0.25 & 14 \\ |
Petermann$^{8}$ & 380 & 900 & 550 & P$_S$ & -0.25 & +0.25 & 14 \\ |
| 379 |
79north$^{9}$ & 70-200 & 900 & 500 & 79Ns & -1.7 & +1.0 & 3 \\ \hline |
79north$^{9}$ & 70-200 & 900 & 500 & 79N$_S$ & -1.7 & +1.0 & 3 \\ \hline |
| 380 |
\end{tabular} |
\end{tabular} |
| 381 |
\caption{Characteristics of several major glacial fjords in Greenland: Main sill (column 2) = depth in meters (NA = not available); Fjord (column 3) = maximum depth of fjord in meters; GL (column 4) = |
\caption{Characteristics of several major glacial fjords in Greenland: Main sill (column 2) = depth in meters (NA = not available); Fjord (column 3) = maximum depth of fjord in meters; GL (column 4) = |
| 382 |
grounding line ice thickness in meters; region in Fig.~1 (column 5); temperature at 250 m depth in 1992-1994 (column 6) corrected by +0.4$^\circ$C in the south, -1$^\circ$C in the northwest and |
grounding line ice thickness in meters; region in Fig.\ 1 (column 5); temperature at 250 m depth in 1992-1994 (column 6) corrected by +0.4$^\circ$C in the south, -1$^\circ$C in the northwest and |
| 383 |
based on {\em in situ} data in the north and north east; change in subsurface temperature in 1992-2009 (column 7) corrected by -1$^\circ$C for King Oscar, -0.25$^\circ$C for Petermann |
based on {\em in situ} data in the north and north east; change in subsurface temperature in 1992-2009 (column 7) corrected by -1$^\circ$C for King Oscar, -0.25$^\circ$C for Petermann |
| 384 |
and unchanged for the other sites, and corresponding increase in subaqueous melt rates of the glaciers (column 8) assuming a linear dependence on thermal forcing from the ocean. |
and unchanged for the other sites, and corresponding increase in subaqueous melt rates of the glaciers (column 8) assuming a linear dependence on thermal forcing from the ocean. |
| 385 |
$^{1}$ Dowdeswell and others (2010); $^{2}$ Andresen and others (2010); $^{3}$ Mortensen and others (2010); $^{4}$ Holland and others (2008); $^{5}$ Rignot and others (2010); |
$^{1}$ Dowdeswell and others (2010); $^{2}$ Andresen and others (2010); $^{3}$ Mortensen and others (2010); $^{4}$ Holland and others (2008); $^{5}$ Rignot and others (2010); |
| 407 |
water velocity (cm/s) at the 250-m depth with location of major ocean currents: Irminger Current (IC), East Greenland Current (EGC), Labrador Current (LC) and West Greenland Current (WGC); |
water velocity (cm/s) at the 250-m depth with location of major ocean currents: Irminger Current (IC), East Greenland Current (EGC), Labrador Current (LC) and West Greenland Current (WGC); |
| 408 |
(c) 2001 mean temperature anomaly at 250 m from the model with respect to the 1992-2009 simulation period; and (d) as (c) but 2009 mean temperature anomaly. Diamonds (triangles) in (a) |
(c) 2001 mean temperature anomaly at 250 m from the model with respect to the 1992-2009 simulation period; and (d) as (c) but 2009 mean temperature anomaly. Diamonds (triangles) in (a) |
| 409 |
indicate the location of on-the-shelf (off-the-shelf) three dimensional boxes used to calculate the yearly-mean subsurface temperatures plotted in Figure 3. Sites are Kangerdlugssuaq Gletscher |
indicate the location of on-the-shelf (off-the-shelf) three dimensional boxes used to calculate the yearly-mean subsurface temperatures plotted in Figure 3. Sites are Kangerdlugssuaq Gletscher |
| 410 |
(Ko and Ks), Southeast Greenland (SEo and SEs), Nuuk (No and Ns), Jakobshavn Isbrae (Jo and Js), Melville Bay (Mo and Ms), Petermann Gletscher (Po and Ps) and 79north Glacier (79No and 79Ns). |
(K$_O$ and K$_S$), Southeast Greenland (SE$_O$ and SE$_S$), Nuuk (N$_O$ and N$_S$), Jakobshavn Isbrae (J$_O$ and J$_S$), Melville Bay (M$_O$ and M$_S$), Petermann Gletscher (P$_O$ and P$_S$) and 79north Glacier (79N$_O$ and 79N$_S$). |
| 411 |
|
|
| 412 |
{\bf Figure 2.} Comparison of subsurface temperature along the AR7W line (see Fig.~1a) in the central Labrador Sea from (a) {\it in situ} data and (b) ECCO2 4-km Arctic Ocean solution for the time period 1992--2009 minus an absolute offset of 0.4$^\circ$C. Similar plots are in (c) and (d), respectively, along the AR7E line in the Irminger Sea (Fig.~1a), and (e) and (f) in the Melville Bay evaluation box (Fig.~1a). |
{\bf Figure 2.} Comparison of subsurface temperature along the AR7W line (see Fig.\ 1a) in the central Labrador Sea from (a) {\it in situ} data and (b) ECCO2 4-km Arctic Ocean solution for the time period 1992--2009 minus an absolute offset of 0.4$^\circ$C. Similar plots are in (c) and (d), respectively, along the AR7E line in the Irminger Sea (Fig.\ 1a), and (e) and (f) in the Melville Bay evaluation box (Fig.\ 1a). |
| 413 |
Triangles in (a), (c), (e) denotes the availability of observations, which are linearly interpolated in between except in (e) between 1991 and 1996. |
Triangles in (a), (c), (e) denotes the availability of observations, which are linearly interpolated in between except in (e) between 1991 and 1996. |
| 414 |
|
|
| 415 |
{\bf Figure 3.} Regional changes in subsurface ocean temperature from the 4-km ECCO2 simulation for the time period 1992--2009 minus an absolute offset of 0.4$^\circ$C. Left column is for off-the-shelf |
{\bf Figure 3.} Regional changes in subsurface ocean temperature from the 4-km ECCO2 simulation for the time period 1992--2009 minus an absolute offset of 0.4$^\circ$C. Left column is for off-the-shelf |
| 416 |
sites (triangle in Fig.~1a); right column is for on-the-shelf sites (diamond in Fig.~1a). The size of the three-dimensional boxes used to calculate annual-mean subsurface temperatures is listed in Table 2. |
sites (triangle in Fig.\ 1a); right column is for on-the-shelf sites (diamond in Fig.\ 1a). The size of the three-dimensional boxes used to calculate annual-mean subsurface temperatures is listed in Table 2. |
| 417 |
Left vertical axis of the plots indicates anomalies in subsurface temperature in reference to the average over the entire time period, between -1.5 and +1.5$^\circ$C, with vertical bars colored in red for |
Left vertical axis of the plots indicates anomalies in subsurface temperature in reference to the average over the entire time period, between -1.5 and +1.5$^\circ$C, with vertical bars colored in red for |
| 418 |
positive anomalies and blue for negative anomalies. Right vertical axis in black is absolute subsurface temperature, with a scale that varies from site to site but not between on-the-shelf and off-the-shelf, |
positive anomalies and blue for negative anomalies. Right vertical axis in black is absolute subsurface temperature, with a scale that varies from site to site but not between on-the-shelf and off-the-shelf, |
| 419 |
except for Ko and Ks. Absolute temperature and anomaly calculations are insensitive to the particular trough or off shelf location near each region ($\pm$ 0.2$^\circ$C) but are somewhat sensitive to |
except for K$_O$ and K$_S$. Absolute temperature and anomaly calculations are insensitive to the particular trough or off shelf location near each region ($\pm$ 0.2$^\circ$C) but are somewhat sensitive to |
| 420 |
the depth range (shelf) and offshore extent (off shelf) over which the calculation is made. Hence, both on and off-shelf averaging volumes use the same depth range - chosen to be below the seasonal |
the depth range (shelf) and offshore extent (off shelf) over which the calculation is made. Hence, both on and off-shelf averaging volumes use the same depth range - chosen to be below the seasonal |
| 421 |
mixed layer and above on-the-shelf waters without significant temporal variability. The off-shelf volumes span the IW component of the boundary current where possible or comparably-sized regions |
mixed layer and above on-the-shelf waters without significant temporal variability. The off-shelf volumes span the IW component of the boundary current where possible or comparably-sized regions |
| 422 |
off the shelf where not (P$_\textrm{s}$). |
off the shelf where not (P$_\textrm{s}$). |
|
\end{document} |
|
| 423 |
|
\end{document} |
Parent Directory
| 
Revision Log
| 
Revision Graph
| 
Patch