Fjords along the western Antarctic Peninsula are episodically exposed to strong winds flowing dow... more Fjords along the western Antarctic Peninsula are episodically exposed to strong winds flowing down marine-terminating glaciers and out over the ocean. These wind events could potentially be an important mechanism for the ventilation of fjord waters. A strong wind event was observed in Andvord Bay in December 2015, and was associated with significant increases in upper-ocean salinity. We examine the dynamical impacts of such wind events during the ice-free summer season using a numerical model. Passive tracers are used to identify water mass pathways and quantify exchange with the outer ocean. Upwelling and outflow in the model fjord generate an average salinity increase of 0.3 in the upper ocean during the event, similar to observations from Andvord Bay. Down-fjord wind events are a highly efficient mechanism for flushing out the upper fjord waters, but have little net impact on deep waters in the inner fjord. As such, summer episodic wind events likely have a large effect on fjord ...
Philosophical transactions. Series A, Mathematical, physical, and engineering sciences, Jan 28, 2018
Palmer Deep canyon along the central West Antarctic Peninsula is known to have higher phytoplankt... more Palmer Deep canyon along the central West Antarctic Peninsula is known to have higher phytoplankton biomass than the surrounding non-canyon regions, but the circulation mechanisms that transport and locally concentrate phytoplankton and Antarctic krill, potentially increasing prey availability to upper-trophic-level predators such as penguins and cetaceans, are currently unknown. We deployed a three-site high-frequency radar network that provided hourly surface circulation maps over the Palmer Deep hotspot. A series of particle release experiments were used to estimate surface residence time and connectivity across the canyon. The majority of residence times fell between 1.0 and 3.5 days, with a mean of 2 days and a maximum of 5 days. We found a highly significant negative relationship between wind speed and residence time. Our residence time analysis indicates that the elevated phytoplankton biomass over the central canyon is transported into and out of the hotspot on time scales m...
The ice cover of the Arctic Ocean is considered to be a sensitive indicator of global climate cha... more The ice cover of the Arctic Ocean is considered to be a sensitive indicator of global climate change. Recent research, using submarine-based observations, suggests that the Arctic ice cover was thinner in the 1990s compared to an earlier period (1958-1979), and that it continued to decrease in thickness in the 1990s. Here I analyze subsurface ice thickness (draft) of Arctic sea ice from six submarine cruises from 1991 to 1997. This extensive data set shows that there was no trend towards a thinning ice cover during the 1990s. Data from the North Pole shows a slight increase in mean ice thickness, whereas the Beaufort Sea shows a small decrease, none of which are significant. Transects between the two areas from 76°N to 90°N also show near constant ice thicknesses, with a general spatial decrease from the Pole towards the Beaufort Sea. Combining the present results with those of an earlier study, I conclude that the mean ice thickness has remained on a near-constant level around the North Pole from 1986 to 1997.
Eos, Transactions American Geophysical Union, 2014
ABSTRACT Understanding the fate and influence of glacial meltwater in heavily ice-covered fjord s... more ABSTRACT Understanding the fate and influence of glacial meltwater in heavily ice-covered fjord systems has proven difficult because previous measurement platforms were constrained to deeper water to keep instrumentation safe from drifting icebergs. Now, using novel, satellite-tracked devices that can with stand multiple collisions with ice blocks (see Figure 1) without incurring much damage, scientists have obtained new and detailed data about the role of Greenland Ice Sheet meltwater and its trajectories through Godthåbsfjord in western Greenland.
Journal of Atmospheric and Oceanic Technology, 2015
ABSTRACT This study investigates the applicability of the optimal interpolation (OI) method propo... more ABSTRACT This study investigates the applicability of the optimal interpolation (OI) method proposed by Kim et al. for estimating ocean surface currents from high-frequency radar (HFR) in the northeastern Chukchi Sea, where HFR siting is dictated by power availability rather than optimal locations. Although the CU technique improves data coverage when compared to the conventional unweighted least squares fit (UWLS) method, biased solutions can emerge. The quality of the HFR velocity estimates derived by OI is controlled by three factors: 1) the number of available incorporating radials (AR), 2) the ratio of the incorporating radials from multiple contributing site locations [ratio of overlapping radial velocities (ROR) or radar geometry], and 3) the positive definiteness [condition number (CN)] of the correlation matrix. Operationally, ROR does not require knowledge of the angle covariance matrix used to compute the geometric dilution of precision (GDOP) in the UWLS method and can be computed before site selection to optimize coverage or after data processing to assess data quality when applying the OI method. The Kim et al. method is extended to examine sensitivities to data gaps in the radial distribution and the effects on OI estimates.
Bulletin of the American Meteorological Society, 2015
ABSTRACT The loss of Arctic sea ice has emerged as a leading signal of global warming. This, toge... more ABSTRACT The loss of Arctic sea ice has emerged as a leading signal of global warming. This, together with acknowledged impacts on other components of the Earth system, has led to the term “The New Arctic”. Global coupled climate models predict that ice loss will continue through the twenty-first century, with implications for governance, economics, security and global weather. A wide range in model projections reflects the complex, highly coupled interactions between the polar atmosphere, ocean and cryosphere, including teleconnections to lower latitudes. This paper summarizes our present understanding of how heat reaches the ice base from the original sources – inflows of Atlantic and Pacific Water, river discharge, and summer sensible heat and shortwave radiative fluxes at the ocean/ice surface – and speculates on how such processes may change in the New Arctic. The complexity of the coupled Arctic system, and the logistic and technological challenges of working in the Arctic Ocean, requires a coordinated interdisciplinary and international program that will not only improve understanding of this critical component of global climate but will also provide opportunities to develop human resources with the skills required to tackle related problems in complex climate systems. We propose a research strategy with components that include: 1) improved mapping of the upper and mid-depth Arctic Ocean, 2) enhanced quantification of important process, 3) expanded long-term monitoring at key heat-flux locations, and 4) development of numerical capabilities that focus on parameterization of heat flux mechanisms and their interactions.
ABSTRACT Most regional ocean models that use discharge as part of the forcing use relatively coar... more ABSTRACT Most regional ocean models that use discharge as part of the forcing use relatively coarse river discharge data sets (1°, or ∼110 km) compared to the model resolution (typically 1/4° or less), and do not account for seasonal changes in river water temperature. We introduce a new climatological data set of river discharge and river water temperature with 1/6° grid spacing over the Arctic region (Arctic River Discharge and Temperature; ARDAT), incorporating observations from 30 Arctic rivers. The annual mean discharge for all rivers in ARDAT is 2817 ± 330 km3 yr-1. River water temperatures range between 0 °C in winter to 14.0 - 17.6 °C in July, leading to a long-term mean monthly heat flux from all rivers of 3.2 ± 0.6 TW, of which 31% is supplied by Alaskan rivers and 69% is supplied by Eurasian rivers. This riverine heat flux is equivalent to 44% of the estimated ocean heat flux associated with the Bering Strait throughflow, but during the spring freshet can be ∼10 times as large, suggesting that heat flux associated with Arctic rivers is an important component of the Arctic heat budget on seasonal time scales.
Fjords along the western Antarctic Peninsula are episodically exposed to strong winds flowing dow... more Fjords along the western Antarctic Peninsula are episodically exposed to strong winds flowing down marine-terminating glaciers and out over the ocean. These wind events could potentially be an important mechanism for the ventilation of fjord waters. A strong wind event was observed in Andvord Bay in December 2015, and was associated with significant increases in upper-ocean salinity. We examine the dynamical impacts of such wind events during the ice-free summer season using a numerical model. Passive tracers are used to identify water mass pathways and quantify exchange with the outer ocean. Upwelling and outflow in the model fjord generate an average salinity increase of 0.3 in the upper ocean during the event, similar to observations from Andvord Bay. Down-fjord wind events are a highly efficient mechanism for flushing out the upper fjord waters, but have little net impact on deep waters in the inner fjord. As such, summer episodic wind events likely have a large effect on fjord ...
Philosophical transactions. Series A, Mathematical, physical, and engineering sciences, Jan 28, 2018
Palmer Deep canyon along the central West Antarctic Peninsula is known to have higher phytoplankt... more Palmer Deep canyon along the central West Antarctic Peninsula is known to have higher phytoplankton biomass than the surrounding non-canyon regions, but the circulation mechanisms that transport and locally concentrate phytoplankton and Antarctic krill, potentially increasing prey availability to upper-trophic-level predators such as penguins and cetaceans, are currently unknown. We deployed a three-site high-frequency radar network that provided hourly surface circulation maps over the Palmer Deep hotspot. A series of particle release experiments were used to estimate surface residence time and connectivity across the canyon. The majority of residence times fell between 1.0 and 3.5 days, with a mean of 2 days and a maximum of 5 days. We found a highly significant negative relationship between wind speed and residence time. Our residence time analysis indicates that the elevated phytoplankton biomass over the central canyon is transported into and out of the hotspot on time scales m...
The ice cover of the Arctic Ocean is considered to be a sensitive indicator of global climate cha... more The ice cover of the Arctic Ocean is considered to be a sensitive indicator of global climate change. Recent research, using submarine-based observations, suggests that the Arctic ice cover was thinner in the 1990s compared to an earlier period (1958-1979), and that it continued to decrease in thickness in the 1990s. Here I analyze subsurface ice thickness (draft) of Arctic sea ice from six submarine cruises from 1991 to 1997. This extensive data set shows that there was no trend towards a thinning ice cover during the 1990s. Data from the North Pole shows a slight increase in mean ice thickness, whereas the Beaufort Sea shows a small decrease, none of which are significant. Transects between the two areas from 76°N to 90°N also show near constant ice thicknesses, with a general spatial decrease from the Pole towards the Beaufort Sea. Combining the present results with those of an earlier study, I conclude that the mean ice thickness has remained on a near-constant level around the North Pole from 1986 to 1997.
Eos, Transactions American Geophysical Union, 2014
ABSTRACT Understanding the fate and influence of glacial meltwater in heavily ice-covered fjord s... more ABSTRACT Understanding the fate and influence of glacial meltwater in heavily ice-covered fjord systems has proven difficult because previous measurement platforms were constrained to deeper water to keep instrumentation safe from drifting icebergs. Now, using novel, satellite-tracked devices that can with stand multiple collisions with ice blocks (see Figure 1) without incurring much damage, scientists have obtained new and detailed data about the role of Greenland Ice Sheet meltwater and its trajectories through Godthåbsfjord in western Greenland.
Journal of Atmospheric and Oceanic Technology, 2015
ABSTRACT This study investigates the applicability of the optimal interpolation (OI) method propo... more ABSTRACT This study investigates the applicability of the optimal interpolation (OI) method proposed by Kim et al. for estimating ocean surface currents from high-frequency radar (HFR) in the northeastern Chukchi Sea, where HFR siting is dictated by power availability rather than optimal locations. Although the CU technique improves data coverage when compared to the conventional unweighted least squares fit (UWLS) method, biased solutions can emerge. The quality of the HFR velocity estimates derived by OI is controlled by three factors: 1) the number of available incorporating radials (AR), 2) the ratio of the incorporating radials from multiple contributing site locations [ratio of overlapping radial velocities (ROR) or radar geometry], and 3) the positive definiteness [condition number (CN)] of the correlation matrix. Operationally, ROR does not require knowledge of the angle covariance matrix used to compute the geometric dilution of precision (GDOP) in the UWLS method and can be computed before site selection to optimize coverage or after data processing to assess data quality when applying the OI method. The Kim et al. method is extended to examine sensitivities to data gaps in the radial distribution and the effects on OI estimates.
Bulletin of the American Meteorological Society, 2015
ABSTRACT The loss of Arctic sea ice has emerged as a leading signal of global warming. This, toge... more ABSTRACT The loss of Arctic sea ice has emerged as a leading signal of global warming. This, together with acknowledged impacts on other components of the Earth system, has led to the term “The New Arctic”. Global coupled climate models predict that ice loss will continue through the twenty-first century, with implications for governance, economics, security and global weather. A wide range in model projections reflects the complex, highly coupled interactions between the polar atmosphere, ocean and cryosphere, including teleconnections to lower latitudes. This paper summarizes our present understanding of how heat reaches the ice base from the original sources – inflows of Atlantic and Pacific Water, river discharge, and summer sensible heat and shortwave radiative fluxes at the ocean/ice surface – and speculates on how such processes may change in the New Arctic. The complexity of the coupled Arctic system, and the logistic and technological challenges of working in the Arctic Ocean, requires a coordinated interdisciplinary and international program that will not only improve understanding of this critical component of global climate but will also provide opportunities to develop human resources with the skills required to tackle related problems in complex climate systems. We propose a research strategy with components that include: 1) improved mapping of the upper and mid-depth Arctic Ocean, 2) enhanced quantification of important process, 3) expanded long-term monitoring at key heat-flux locations, and 4) development of numerical capabilities that focus on parameterization of heat flux mechanisms and their interactions.
ABSTRACT Most regional ocean models that use discharge as part of the forcing use relatively coar... more ABSTRACT Most regional ocean models that use discharge as part of the forcing use relatively coarse river discharge data sets (1°, or ∼110 km) compared to the model resolution (typically 1/4° or less), and do not account for seasonal changes in river water temperature. We introduce a new climatological data set of river discharge and river water temperature with 1/6° grid spacing over the Arctic region (Arctic River Discharge and Temperature; ARDAT), incorporating observations from 30 Arctic rivers. The annual mean discharge for all rivers in ARDAT is 2817 ± 330 km3 yr-1. River water temperatures range between 0 °C in winter to 14.0 - 17.6 °C in July, leading to a long-term mean monthly heat flux from all rivers of 3.2 ± 0.6 TW, of which 31% is supplied by Alaskan rivers and 69% is supplied by Eurasian rivers. This riverine heat flux is equivalent to 44% of the estimated ocean heat flux associated with the Bering Strait throughflow, but during the spring freshet can be ∼10 times as large, suggesting that heat flux associated with Arctic rivers is an important component of the Arctic heat budget on seasonal time scales.
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Papers by Peter Winsor