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  • Drake Passage  (2)
  • Glacier
  • 1
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    Molecular characterization of dissolved organic matter associated with the Greenland ice sheet (2010)
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    Publication Date: 2022-05-25
    Description: Author Posting. © The Author(s), 2010. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Geochimica et Cosmochimica Acta 74 (2010): 3768-3784, doi:10.1016/j.gca.2010.03.035.
    Description: Subsurface microbial oxidation of overridden soils and vegetation beneath glaciers and ice sheets may affect global carbon budgets on glacial-interglacial timescales. The likelihood and magnitude of this process depends on the chemical nature and reactivity of the subglacial organic carbon stores. We examined the composition of carbon pools associated with different regions of the Greenland ice sheet (subglacial, supraglacial, proglacial) in order to elucidate the type of dissolved organic matter (DOM) present in the subglacial discharge over a melt season. Electrospray ionization (ESI) Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry coupled to multivariate statistics permitted unprecedented molecular level characterization of this material and revealed that carbon pools associated with discrete glacial regions are comprised of different compound classes. Specifically, a larger proportion of protein-like compounds were observed in the supraglacial samples and in the early melt season (spring) subglacial discharge. In contrast, the late melt season (summer) subglacial discharge contained a greater fraction of lignin-like and other material presumably derived from underlying vegetation and soil. These results suggest (1) that the majority of supraglacial DOM originates from autochthonous microbial processes on the ice sheet surface, (2) that the subglacial DOM contains allochthonous carbon derived from overridden soils and vegetation as well as autochthonous carbon derived from in situ microbial metabolism, and (3) that the relative contribution of allochthonous and autochthonous material in subglacial discharge varies during the melt season. These conclusions are consistent with the hypothesis that, given sufficient time (e.g., overwinter storage), resident subglacial microbial communities may oxidize terrestrial material beneath the Greenland ice sheet.
    Description: This research was supported by: the National Science Foundation (CAREER-OCE- 0529101 (EBK), ARC-0520077 (SBD)), National Atmospheric and Space Administration (SBD), the WHOI Clark Arctic Research Initiative (EBK, SBD, MAC), the WHOI Ocean Ventures Fund (MPB), and the National and Science Engineering Research Council of Canada (MPB).
    Keywords: Glacier ; Ultrahigh resolution mass spectrometry ; FT-ICR ; Organic carbon ; DOM
    Repository Name: Woods Hole Open Access Server
    Type: Preprint
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  • 2
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    Winter mesoscale circulation on the shelf slope region of the southern Drake Passage (2013)
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    Publication Date: 2022-05-25
    Description: Author Posting. © The Author(s), 2013. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part II: Topical Studies in Oceanography 90 (2013): 4-14, doi:10.1016/j.dsr2.2013.03.041.
    Description: An austral winter cruise in July-August 2006 was conducted to study the winter circulation and iron delivery processes in the Southern Drake Passage and Bransfield Strait. Results from current and hydrographic measurements revealed a circulation pattern similar to that of the austral summer season observed in previous studies: The Shackleton Transverse Ridge (STR) in the southern Drake Passage blocks a part of the eastward Antarctic Circumpolar Current (ACC) which forces the ACC to detour southward, produces a Taylor Column over the STR, and forms an ACC jet within the Shackleton Gap, a deep channel between the STR and the shelf of Elephant Island. Observations show that to the west of the STR, the Upper Circumpolar Deep Water (UCDW) intruded onto the shelf around the South Shetland Islands while to the east of the STR, shelf waters were transported off the northern shelf of Elephant Island. Along a similar west-east transect approximately 50 km off the shelf, the northward transport of shelf waters was approximately 2.4 and 1.2 Sv in the austral winter and summer, respectively. The waters around Elephant Island primarily consist of the UCDW that has been modified by local cooling and freshening, unmodified UCDW that has recently intruded onto the shelf, and Bransfield Current water that is a mixture of shelf and Bransfield Strait waters. Weddell Sea outflows were observed which affect the hydrography and circulation in the Bransfield Strait and indirectly affect the circulation patterns in the southern Drake Passage and around Elephant Island. Two Fe enrichment and transport mechanisms are proposed that intrusions of the UCDW onto the northern shelf region of the South Shetland Islands is considered as the results of Ekman pumping due to prevailing westerly wind in the region while the offshelf transport of shelf waters in the shelf region east of Elephant Island is due to acquisition of positive vorticity by shelf waters from horizontal mixing with onshelf intruded ACC waters.
    Description: This project was supported by the National Science Foundation grant numbers OPP-0229966, ANT-0444040 and ANT-0948378 to M. Zhou, OPP0230445, ANT0443403 and ANT-0948357 to C. Measures, ANT0443869 and ANT-0948442 to M. Charette, and OPP0230443, ANT0444134 and ANT0948338 to B.G. Mitchell.
    Keywords: Southern Ocean ; Drake Passage ; Antarctic Circumpolar Current ; Shelf waters ; Mesoscale eddies ; Mixing ; Iron transport
    Repository Name: Woods Hole Open Access Server
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  • 3
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    Utility of Rn-222 as a passive tracer of subglacial distributed system drainage (2017)
    Elsevier
    Details
    Publication Date: 2022-05-25
    Description: This paper is not subject to U.S. copyright. The definitive version was published in Earth and Planetary Science Letters 462 (2017): 180-188, doi:10.1016/j.epsl.2016.12.039.
    Description: Water flow beneath the Greenland Ice Sheet (GrIS) has been shown to include slow-inefficient (distributed) and fast-efficient (channelized) drainage systems, in response to meltwater delivery to the bed via both moulins and surface lake drainage. This partitioning between channelized and distributed drainage systems is difficult to quantify yet it plays an important role in bulk meltwater chemistry and glacial velocity, and thus subglacial erosion. Radon-222, which is continuously produced via the decay of 226Ra, accumulates in meltwater that has interacted with rock and sediment. Hence, elevated concentrations of 222Rn should be indicative of meltwater that has flowed through a distributed drainage system network. In the spring and summer of 2011 and 2012, we made hourly 222Rn measurements in the proglacial river of a large outlet glacier of the GrIS (Leverett Glacier, SW Greenland). Radon-222 activities were highest in the early melt season (10–15 dpm L−1), decreasing by a factor of 2–5 (3–5 dpm L−1) following the onset of widespread surface melt. Using a 222Rn mass balance model, we estimate that, on average, greater than 90% of the river 222Rn was sourced from distributed system meltwater. The distributed system 222Rn flux varied on diurnal, weekly, and seasonal time scales with highest fluxes generally occurring on the falling limb of the hydrograph and during expansion of the channelized drainage system. Using laboratory based estimates of distributed system 222Rn, the distributed system water flux generally ranged between 1–5% of the total proglacial river discharge for both seasons. This study provides a promising new method for hydrograph separation in glacial watersheds and for estimating the timing and magnitude of distributed system fluxes expelled at ice sheet margins.
    Description: U.S. National Science Foundation Arctic Natural Sciences Program (ANS-1256669); Woods Hole Oceanographic Institution Arctic Research Initiative, Ocean Ventures Fund, and Ocean Climate Change Institute; United Kingdom Natural Environment Research Council studentship (NE/152830X/1); the Carnegie Trust, Edinburgh University Development Trust.
    Keywords: Radon ; Greenland ; Glacier ; Proglacial river ; Meltwater
    Repository Name: Woods Hole Open Access Server
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  • 4
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    Seasonal cycle of circulation in the Antarctic Peninsula and the off-shelf transport of shelf waters into southern Drake Passage and Scotia Sea (2013)
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © The Author(s), 2013. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part II: Topical Studies in Oceanography 90 (2013): 15-30, doi:10.1016/j.dsr2.2013.02.029.
    Description: The seasonal cycle of circulation and transport in the Antarctic Peninsula shelf region is investigated using a high-resolution (~2km) regional model based on the Regional Oceanic Modeling System (ROMS). The model also includes a naturally occurring tracer with a strong source over the shelf (radium isotope 228Ra, t1/2=5.8 year) to investigate the sediment Fe input and its transport. The model is spun up for three years using climatological boundary and surface forcing and then run for the 2004-2006 period using realistic forcing. Model results suggest a persistent and coherent circulation system throughout the year consisting of several major components that converge water masses from various sources toward Elephant Island. These currents are largely in geostrophic balance, driven by surface winds, topographic steering, and large-scale forcing. Strong off-shelf transport of the Fe-rich shelf waters takes place over the northeastern shelf/slope of Elephant Island, driven by a combination of topographic steering, extension of shelf currents, and strong horizontal mixing between the ACC and shelf waters. These results are generally consistent with recent and historical observational studies. Both the shelf circulation and off-shelf transport show a significant seasonality, mainly due to the seasonal changes of surface winds and large-scale circulation. Modeled and observed distributions of 228Ra suggest that a majority of Fe-rich upper layer waters exported off-shelf around Elephant Island are carried by the shelfbreak current and the Bransfield Strait Current from the shallow sills between Gerlache Strait and Livingston Island, and northern shelf of the South Shetland Islands, where strong winter mixing supplies much of the sediment derived nutrients (including Fe) input to the surface layer.
    Description: This project is supported by NOAA grant NA09OAR4310062. MZ and MJ 11 are also supported by NSF grant 0948378 and MAC by NSF grant 0948442.
    Keywords: Model ; Circulation ; Antarctic Peninsula ; Antarctic Circumpolar Current ; Elephant Island ; Off-shelf transport ; Fe ; Drake Passage ; Southern Scotia Sea
    Repository Name: Woods Hole Open Access Server
    Type: Preprint
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