148 research outputs found
Submarine melt rates, plume dynamics, hydrography, and ice base topography at 79NG
No full textThe zip file contains:
- Submarine melt rates and plume dynamics at 79NG simulated using the 1D Ice Shelf Water plume model from Jenkins, 1991 (STANDARDrun60.dat).
- Hydrography measured in the cavity of the 79NG using a CTD as obtained in September 2009 by Wilson and Straneo, 2015 (ctd23.dat).
- Processed ice base topography along the centreline of the 79NG, modified from RTopo2, Schaffer et al., 2016 (ice_base_topography.dat).
- 1D ISW plume model based on Jenkins, 1991; Smedsrud and Jenkins, 2004; Jenkins, 2011 (.mat).
- MATLAB script to plot submarine melt rates and plume dynamics (plot_it.mat)
Recommended from our members
Ocean Dynamics of Greenland’s Glacial Fjords at Subannual to Seasonal Timescales
Get PDFMass loss of the Greenland Ice Sheet is expected to accelerate in the 21st century in response to both a warming atmosphere and ocean, with consequences for sea level rise, polar ecosystems and potentially the global overturning circulation. Glacial fjords connect Greenland’s marine-terminating glaciers with the continental shelf, and fjord circulation plays a critical role in modulating the import of heat from the ocean and the export of freshwater from the ice sheet. Understanding fjord dynamics is crucial to predicting the cryosphere and ocean response to a changing climate. However, representing glacial fjord dynamics in climate models is an ongoing challenge because fjord circulation is complex and sensitive to glacial forcing that is poorly understood. Additionally, there are limited observations available for constraining models and theory. This dissertation aims to improve our understanding of fjord dynamics, focusing on key aspects (heat variability, freshwater residence time, and fjord exchange) which need to be included in glacial fjord parameterizations.We use three approaches combining novel observations, idealized, modeling and numerical simulations to investigate the dynamics of fjord circulation at different spatial scales. First, we investigate the heat content variability in the fjord using acoustic travel time (Chapter 2). We demonstrate that acoustic travel time can be used to model fjord stratification during winter months and monitor heat content variability at synoptic and seasonal timescales. Secondly, we use a combination of in situ observations and an idealized box model to evaluate freshwater residence time in a west Greenland Fjord (Chapter 3). We find that meltwater from the ice sheet is mixed downward across multiple layers near the glacier terminus resulting in freshwater storage and a delay in freshwater export from the fjord. Finally we analyze a multi-year realistically forced numerical simulation of Sermilik Fjord in southeast Greenland and identify the impact of shelf and glacial forcing on fjord exchange (Chapter 4). We show that the glacial-driven circulation is more efficient at renewing the fjord and that the sign of the exchange flow is related to the along-shelf wind stress. This dissertation strengthens our understanding of the fundamental connections between oceans and glaciers, and will lead to improved representation of ice-ocean interactions in climate models
Recommended from our members
A Comparison of Moored Acoustic Doppler Profiler Data and Satellite Altimeter Data on the Variability of East Greenland Current from 2016-2020
Get PDFThe East Greenland Current (EGC) and the East Greenland Coastal Current (EGCC) are part of the North Atlantic Ocean circulation system that carries cold fresh melting water from the Arctic southward to the Subpolar North Atlantic region; hence, determining the variability and the drivers of these currents can help scientists to develop a better understanding of the circulation and climate in the Northern Hemisphere. In this study, we compare velocity from Acoustic Doppler Current Profilers (ADCP) data (2016-2020) from the Overturning in the Subpolar North Atlantic Program (OSNAP) moorings deployed near the Cape Farewell, at the southern tip of Greenland, with the geostrophic velocity derived from satellite altimeter data from AVISO that measures the sea level anomalies (SLA). The goal is to determine which part of the moored observed variability can be derived from the altimeter data. It is found that the seasonal variability observed via the two methods is similar. Similarly, the magnitude of across flow velocity anomaly of the two data sets are the same, but the along flow velocity anomaly computed from the satellite altimeter data is slightly smaller than that of the mooring data. Overall, our results suggest that the satellite altimeter is a complementary tool for ocean circulation observation at high latitudes where moorings are not deployed
Surface total dissolvable iron data collected during an August 2015 cruise to Sermilik Fjord, East Greenland
No full textThis dataset contains discrete total dissolvable iron (TdFe) data collected from the surface of Sermilik Fjord in SE Greenland in August 2015 aboard the RV Adolf Jensen. Surface samples were collected using a trace metal clean sampler fixed to a plastic pole. Samples were taken while the ship was steaming at approximately 1 knot in order to minimize contamination from the ship. All bottles and plasticware were cleaned using trace metal clean procedures outlined in the U.S. GEOTRACES protocols. Unfiltered samples were placed in separate trace metal clean 250 mL low-density polyethylene bottles and immediately acidified to pH 1.8 with 4 mL Optima HCl (Fisher Scientific) and stored until analysis using standard addition methods and cathodic stripping voltammetry 4 months later in the lab at the Woods Hole Oceanographic Institution
Hydrographic sensor and bottle data collected during an August 2015 cruise to Sermilik Fjord, East Greenland
No full textThis dataset contains hydrographic observations from Sermilik Fjord in SE Greenland, collected in August 2015 aboard the RV Adolf Jensen, including discrete data derived from water sample analyses and corresponding CTD sensor data. CTD data were collected using a Seabird 25Plus Sealogger equipped with a SBE 43 dissolved oxygen sensor, a Satlantic PAR LOG sensor, and a Wetlabs / Seabird ECO Triplet (chlorophyll-a and CDOM fluorescence, as well as backscattering at 700 nm). Discrete samples for nitrate, phosphate, silicate, and ammonium, were filtered through a sterile 0.22 µM Sterivex filter using standard protocols and kept frozen at -20 °C for later analysis at the Woods Hole Oceanographic Institution Nutrient Analytical Facility. Dissolved nutrient concentrations were quantified using a SEAL AA3 four-channel segmented flow analyzer
Recommended from our members
Interannual Variability of Sea Ice Area and Volume in the Greenland Sea
Get PDFArctic sea ice loss continues to serve as a strong gauge of climate change. It is the component of the Earth system that is responding most visibly and rapidly to a warming climate. The implications of a shrinking sea ice cover include changes in physical processes like deep water formation and the reflection of solar radiation, and alterations to the way of live for humans and animals that depend on the ice in their daily lives. Here I evaluate long term trends in sea ice coverage in the Greenland Sea and Irminger Basin from 1979 to 2018. While in the Arctic Basin the recession of summer sea ice is more pronounced, it is shown that in the Greenland Sea the declining winter sea ice maximum is more pronounced than the summertime reduction. The strongest signature of this robust trend is the disappearance in 2004 of a sea ice feature called the Odden Ice Tongue that is characterized by local freezing and ice formation and to a lesser extent by the advection of sea ice. A budget constructed from sea ice concentration and velocity estimates from the National Snow and Ice Data Center, and sea ice thickness estimates from the University of Washington’s Pan-Arctic Ice Ocean Modeling and Assimilation System indicates that the area of sea ice transported into the Greenland Sea from the Arctic has gone largely unchanged since measurements began in late 1978. Despite this, the volume of sea ice flowing out of the Arctic has decreased 11% when compared to the 1979-2004 mean due to a significant thinning of sea ice. In the last 15 years the average winter buildup of sea ice volume in the Greenland Sea is 16% smaller than the same winter accumulation from 1979 to 2004. The volume of sea ice that is advected into the Greenland Sea, from Fram Strait, is approximately twice as large as the change in volume of sea ice in the area over the course of a typical winter, indicating that half of the advected sea ice melts over the course of the winter
Recommended from our members
Nutrient compositions in southeast Greenland waters and polar water influence on distribution
Get PDFThe convergence of freshwater from polar and subpolar waters influences nutrient (nitrate, phosphate, and silicate) concentrations on the southeastern Greenland shelf. Interannual variability of nutrient distributions from the shoreline to 150 km offshore were determined by using hydrographic and nutrient measurements from June to September of 2002 to 2016 to produce high-resolution transects. Although no significant trend was observed during the period analyzed, in-situ observations from 1991 to 2018 revealed considerable interannual variability and that nutrient concentrations in polar-origin waters (POLW) were two to three times less than those of Atlantic-origin (AW). In POLW, the mean nitrate, phosphate, and silicate concentrations (in µmol/kg) were 5.02, 0.51, and 3.10, respectively, compared to that of AW, with means of 15.16, 0.98, and 7.80, respectively over the same area. Waters of Pacific-origin, transported through the Arctic Ocean circulation and western Fram Strait, were observed furthest inshore in southeastern Greenland from 1997 to 2018 with increased fractions of Pacific Water concentration in 2004 (0.15) and 2018 (0.16). From relationships observed between nutrients, nitrate was identified as the least biologically-available nutrient, followed by phosphate, and then, silicate, which concurred with previous studies in the North Atlantic region. The accepted global stochiometric relationships for N:P, N:Si, and Si:P are 16, 1.07, and 15, respectively. As expected, results differed slightly throughout the cross section, as the area from the shoreline to 72 km exhibited ratios of 17.71, 1.66, and 9.70, respectively, while the area from 72 km to 150 displayed ratios of 13.56, 1.00, and 10.14, respectively
Satellite-derived submarine melt rates and mass balance (2011–2015) for Greenland's largest remaining ice tongues
Get PDF© The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in The Cryosphere 11 (2017): 2773-2782, doi:10.5194/tc-11-2773-2017.Ice-shelf-like floating extensions at the termini of Greenland glaciers are undergoing rapid changes with potential implications for the stability of upstream glaciers and the ice sheet as a whole. While submarine melting is recognized as a major contributor to mass loss, the spatial distribution of submarine melting and its contribution to the total mass balance of these floating extensions is incompletely known and understood. Here, we use high-resolution WorldView satellite imagery collected between 2011 and 2015 to infer the magnitude and spatial variability of melt rates under Greenland's largest remaining ice tongues – Nioghalvfjerdsbræ (79 North Glacier, 79N), Ryder Glacier (RG), and Petermann Glacier (PG). Submarine melt rates under the ice tongues vary considerably, exceeding 50 m a−1 near the grounding zone and decaying rapidly downstream. Channels, likely originating from upstream subglacial channels, give rise to large melt variations across the ice tongues. We compare the total melt rates to the influx of ice to the ice tongue to assess their contribution to the current mass balance. At Petermann Glacier and Ryder Glacier, we find that the combined submarine and aerial melt approximately balances the ice flux from the grounded ice sheet. At Nioghalvfjerdsbræ the total melt flux (14.2 ± 0.96 km3 a−1 w.e., water equivalent) exceeds the inflow of ice (10.2 ± 0.59 km3 a−1 w.e.), indicating present thinning of the ice tongue.Nat Wilson, Fiammetta Straneo, and
Patrick Heimbach were supported by NASA NNX13AK88G
and NSF OCE 1434041
On the effect of a sill on dense water formation in a marginal sea
Get PDFAuthor Posting. © Sears Foundation for Marine Research, 2008. This article is posted here by permission of Sears Foundation for Marine Research for personal use, not for redistribution. The definitive version was published in Journal of Marine Research 66 (2008): 325-345, doi:10.1357/002224008786176016.The properties of water mass transformation in a semi-enclosed basin, separated from the open ocean by a sill and subject to surface cooling, are analyzed both theoretically and numerically using an ocean general circulation model. This study extends previous studies of convection in a marginal sea to the case with a sill.
The sill has a strong impact on both the properties of the dense water formed in the interior and on those of the waters flowing out the marginal sea. It results in a colder interior and colder outflow compared to the case with no sill. Dynamically, this is explained by considering that the sill limits the geostrophic contours over which the open ocean/marginal sea exchange can occur. The impact of the sill, however, is not simply limited to a topographic constriction; instead the sill also decreases the stability of the boundary current, which, in turn, results in relatively large heat flux into the interior and colder outflow.
The theories that relate the properties of the dense waters formed in the interior, and those of the outflow, are modified to include the impact of the sill. These are found to compare well with the numerical simulations and provide a useful tool for the interpretation of these results. These idealized simulations capture the basic features of the water mass transformation processes in the Nordic Seas and, in particular, provide a dynamical explanation for the difference between the dense waters formed and the source of the overflows water.DI was supported by the Polar Ocean Climate Processes (ProClim) project
funded by the Norwegian Research Council. FS was supported by a visiting scientist fellowship from
the Bjerknes Centre for Climate Research (Bergen, Norway) and by NSF Ocean Sciences Grant
0525929. Support for MAS was provided by NSF Office of Polar Programs Grant 0421904 and NSF
Ocean Sciences Grant 0423975
Profiles of temperature, salinity, and turbidity from Sermilik Fjord and Kangerlussuaq Fjord during September 2012
No full text- …
