Iceberg drift and ocean circulation in the northwestern Weddell Sea, Antarctica

Collares, Lorena Luiz; Mata, Maurício M.; Kerr, Rodrigo; Arigony-Neto, Jorge; Barbat, Mauro M.

doi:10.1016/j.dsr2.2018.02.014

Cited by 43 publications

(50 citation statements)

References 70 publications

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“…The borders of the Southern Ocean sectors and location of ice shelves discussed in this work are also shown. (Collares et al, 2018;Gladstone, 2001;Schodlok et al, 2006).…”

Section: Iceberg Spatial Distributionmentioning

confidence: 99%

Three Years of Near‐Coastal Antarctic Iceberg Distribution From a Machine Learning Approach Applied to SAR Imagery

et al. 2019

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Mass loss around the Antarctic Ice Sheet is driven by basal melting and iceberg calving, which constitute the two dominant paths of freshwater flux into the Southern Ocean. Although of similar magnitude, icebergs play an important and still not fully understood role in the balance of heat and freshwater around Antarctica. This lack of understanding is partly due to operational difficulties in large-scale monitoring in polar regions, despite observational and remote sensing efforts. In this study, a novel machine learning approach, augmented by visual inspection, was applied to three Synthetic Aperture Radar (SAR) mosaics of the whole Antarctic continent and its adjacent coastal zone. Although originally intended for a mapping of the Antarctic continent, the SAR mosaics allow us to document the evolution and distribution of the size (and mass) of icebergs in the pan-Antarctic near-coastal zone for the years 1997, 2000, and 2008. Our novel algorithm identified 7,649 icebergs in 1997, 13,712 icebergs in 2000, and 7,246 icebergs in 2008 with surface areas between 0.1 and 4,567.82 km 2 and total masses of 4,641.53, 6,862.81, and 5,263.69 Gt, respectively. Large regional variability was observed, although a zonal pattern distribution is present. This has implications for future climate modeling studies that try to estimate the freshwater flux from melting icebergs, which demands a realistic representation of the interannually varying near-coastal iceberg pattern to initialize the simulations. Plain Language SummaryWhen icebergs melt in the Southern Ocean, they cool the surrounding ocean. They also distribute freshwater, which potentially impacts the circulation, biological activity, sea-ice cover, and the formation of the densest waters of the world's oceans. However, all these influences are not fully understood because we are lacking reliable methods to detect icebergs from space via satellites. This study has the main objective to determine how iceberg mass is distributed in the coastal zone around the Antarctic continent and how this distribution changes between individual years. We show that a novel machine learning approach can be applied to this problem, which is capable to identify icebergs in satellite images of the near-coastal ocean region almost automatically. The method also works in severe conditions, e.g. when the icebergs are affected by ocean waves or when they are surrounded by sea ice. Our results complement the ongoing discussion about the distribution of Antarctic icebergs in open-ocean regions that are not affected by sea ice. The resulting data can also be used in computer models that simulate the input of iceberg freshwater into the ocean.

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“…The borders of the Southern Ocean sectors and location of ice shelves discussed in this work are also shown. (Collares et al, 2018;Gladstone, 2001;Schodlok et al, 2006).…”

Section: Iceberg Spatial Distributionmentioning

confidence: 99%

Three Years of Near‐Coastal Antarctic Iceberg Distribution From a Machine Learning Approach Applied to SAR Imagery

et al. 2019

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“…The circulation within the Bransfield Strait is characterized by a cyclonic gyre [e.g., Zhou et al ., ; Sangrà et al ., ]. The cold waters from the continental shelf of the Weddell Sea flow into the region around the tip of the Antarctic Peninsula and Joinville Island (Figure a) [ von Gyldenfeldt et al ., ; Thompson et al ., ; Collares et al ., ], whereas Circumpolar Deep Water (CDW) and warm surface waters from the Bellingshausen Sea enter into the Bransfield Strait mainly at the southwestern passages between (i) the Snow, Smith and Low Islands and the Antarctic Peninsula [ Niiler et al ., ] and between (ii) King George and Elephant Islands (Figure a) [ Hofmann et al ., ]. This complex combination of water masses characterizes the thermohaline properties and variability of the deep waters of the Bransfield Strait [e.g., Clowes , ; Gordon and Nowlin , ; Hofmann et al ., ; Wilson et al ., ; Gordon et al ., ; Garcia and Mata , ].…”

Section: Introductionmentioning

confidence: 99%

Multidecadal freshening and lightening in the deep waters of the Bransfield Strait, Antarctica

et al. 2016

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The deep waters of the Bransfield Strait receive considerable amounts of water from the Weddell Sea continental shelf. The restricted connections to the surrounding ocean and relatively easier access makes the Bransfield Strait an important proxy region for monitoring changes in the dense Weddell Sea shelf water masses, which are an important precursor of Antarctic Bottom Water (AABW). Long‐term hydrographic data from the period 1960s–2010s showed freshening and lightening of the deep water masses of the Bransfield Strait, which was likely caused by large freshwater inputs originating from the western shelf of the Weddell Sea. The rates of freshening and lightening were −0.0010 ± 0.0005 yr−1 and −0.0016 ± 0.0014 kg m−3 yr−1 for the central basin, respectively, and −0.0010 ± 0.0006 yr−1 and −0.0029 ± 0.0013 kg m−3 yr−1 for the eastern basin, respectively. The deep waters showed a high degree of interannual thermohaline variability, which appeared to be caused by changes in the proportions of source water mass mixing between the years. Statistically significant negative correlations between salinity/neutral density fields and the Southern Annular Mode (SAM) were observed (−0.56 and −0.62 for the central basin, respectively, and −0.58 and −0.68 for the eastern basin, respectively) between 1980 and 2014. During SAM positive phases, communication between the Weddell Sea and the Bransfield Strait is reduced, which leads to less saline and lighter water masses in the Bransfield Strait; however, the opposite trends are observed during SAM negative phases.

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“…In the eastern part, transitional water from the Weddell Sea (Transitional Weddell Sea Water, TWW) enters the Bransfield Strait through the Antarctic Sound and from the Antarctic Peninsula (AP). This water mass corresponds to the Antarctic Coastal Current (Collares et al, 2018;Thompson et al, 2009). The TWW is significantly colder (summer SST < 0 • C) and saltier due to extended sea ice formation in the Weddell Sea Gyre.…”

Section: Oceanographic Settingmentioning

confidence: 99%

“…In previous studies, an HBI triene (HBI C 25:3 ; Fig. 1b-c) found in polar and sub-polar phytoplankton samples (Massé et al, 2011) has been considered alongside IPSO 25 , and the ratio of IPSO 25 to this HBI triene has hence been interpreted as a measure for the relative contribution of organic matter derived from sea ice algae versus open water phytoplankton (Massé et al, 2011;Collins et al, 2013;Etourneau et al, 2013;Barbara et al, 2013Barbara et al, , 2016. Collins et al (2013) further suggested that the HBI triene might reflect phytoplankton productivity in marginal ice zones (MIZs) and, based on the observation of elevated HBI triene concentrations in East Antarctic MIZ surface waters, this has been strengthened by Smik et al (2016a).…”

Section: Introductionmentioning

confidence: 99%

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Highly branched isoprenoids for Southern Ocean sea ice reconstructions: a pilot study from the Western Antarctic Peninsula

et al. 2019

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Abstract. Organic geochemical and micropaleontological analyses of surface sediments collected in the southern Drake Passage and the Bransfield Strait, Western Antarctic Peninsula, enable a proxy-based reconstruction of recent sea ice conditions in this climate-sensitive area. We study the distribution of the sea ice biomarker IPSO25, and biomarkers of open marine environments such as more unsaturated highly branched isoprenoid alkenes and phytosterols. Comparison of the sedimentary distribution of these biomarker lipids with sea ice data obtained from satellite observations and diatom-based sea ice estimates provide for an evaluation of the suitability of these biomarkers to reflect recent sea surface conditions. The distribution of IPSO25 supports earlier suggestions that the source diatom seems to be common in near-coastal environments characterized by annually recurring sea ice cover, while the distribution of the other biomarkers is highly variable. Offsets between sea ice estimates deduced from the abundance of biomarkers and satellite-based sea ice data are attributed to the different time intervals recorded within the sediments and the instrumental records from the study area, which experienced rapid environmental changes during the past 100 years. To distinguish areas characterized by permanently ice-free conditions, seasonal sea ice cover and extended sea ice cover, we apply the concept of the PIP25 index from the Arctic Ocean to our data and introduce the term PIPSO25 as a potential sea ice proxy. While the trends in PIPSO25 are generally consistent with satellite sea ice data and winter sea ice concentrations in the study area estimated by diatom transfer functions, more studies on the environmental significance of IPSO25 as a Southern Ocean sea ice proxy are needed before this biomarker can be applied for semi-quantitative sea ice reconstructions.

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Iceberg drift and ocean circulation in the northwestern Weddell Sea, Antarctica

Cited by 43 publications

References 70 publications

Three Years of Near‐Coastal Antarctic Iceberg Distribution From a Machine Learning Approach Applied to SAR Imagery

Three Years of Near‐Coastal Antarctic Iceberg Distribution From a Machine Learning Approach Applied to SAR Imagery

Multidecadal freshening and lightening in the deep waters of the Bransfield Strait, Antarctica

Highly branched isoprenoids for Southern Ocean sea ice reconstructions: a pilot study from the Western Antarctic Peninsula

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