Glacier tongue calving reduced dense water formation and enhanced carbon uptake

Shadwick, E. H.; Rintoul, Stephen R.; Tilbrook, Bronte; Williams, Guy D.; Young, Neal W.; Fraser, Alexander; Marchant, Harvey J.; Smith, J. A.; Tamura, Takeshi

doi:10.1002/grl.50178

Cited by 83 publications

(123 citation statements)

References 48 publications

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“…In 2005, when the abovedescribed pattern was particularly conspicuous, high Chl a (up to 20 µg L −1 ) in the southern coastal area of the sampling grid provides further evidence that high primary productivity led to the observed high arag despite the presence of freshwater. Similar results were found after the calving event of the Mertz Glacier tongue in eastern Antarctica, where enhanced primary productivity increased the arag and thereby counteracted the effect of dilution by meltwater input (Shadwick et al, 2013).…”

Section: Parametersupporting

confidence: 78%

Two decades of inorganic carbon dynamics along the West Antarctic Peninsula

et al. 2015

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Abstract. We present 20 years of seawater inorganic carbon measurements collected along the western shelf and slope of the Antarctic Peninsula. Water column observations from summertime cruises and seasonal surface underway pCO 2 measurements provide unique insights into the spatial, seasonal, and interannual variability in this dynamic system. Discrete measurements from depths > 2000 m align well with World Ocean Circulation Experiment observations across the time series and underline the consistency of the data set. Surface total alkalinity and dissolved inorganic carbon data showed large spatial gradients, with a concomitant wide range of arag (< 1 up to 3.9). This spatial variability was mainly driven by increasing influence of biological productivity towards the southern end of the sampling grid and meltwater input along the coast towards the northern end. Large inorganic carbon drawdown through biological production in summer caused high near-shore arag despite glacial and seaice meltwater input. In support of previous studies, we observed Redfield behavior of regional C / N nutrient utilization, while the C / P (80.5 ± 2.5) and N / P (11.7 ± 0.3) molar ratios were significantly lower than the Redfield elemental stoichiometric values. Seasonal salinity-based predictions of arag suggest that surface waters remained mostly supersaturated with regard to aragonite throughout the study. However, more than 20 % of the predictions for winters and springs between 1999 and 2013 resulted in arag < 1.2. Such low levels of arag may have implications for important organisms such as pteropods. Even though we did not detect any statistically significant long-term trends, the combination of ongoing ocean acidification and freshwater input may soon induce more unfavorable conditions than the ecosystem experiences today.

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Section: Parametersupporting

confidence: 78%

Two decades of inorganic carbon dynamics along the West Antarctic Peninsula

et al. 2015

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“…Shadwick et al [2013] link the freshening of 0.15 of the dense shelf water observed in the Ad elie Depression between 2008 and 2011 to reduced sea ice production in the reshaped MGP after the Mertz Glacier calving. Studying the impact of the glacier calving on ice production in the MGP, Tamura et al [2012] indeed found that annual sea ice production in the polynya extending over the Ad elie Depression and the Mertz Depression had reduced by 14% and 20% in 2010 and 2011, respectively, out of an annual mean of approximately 170 km 3 estimated over the precalving period (2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009).…”

Section: Introductionmentioning

confidence: 90%

“…Glacial melt may arise from enhanced contact of land or sea ice with relatively warm water, especially with the Modified Circumpolar Deep Water (MCDW) intruding on the shelf. Although there is no evidence that such a process did impact on the dense shelf water freshening observed in summer 2011 in the Ad elie Depression, Shadwick et al [2013] suggest that it may have contributed to the 1.16 m excess of freshwater added to the top 200 m of the Ad elie Depression in that year, as a result of more ice being advected and melted into the region after the removal of the Mertz ''barrier.'' With regards to dense water production, surface freshening increases the upper ocean vertical stability which in late summer-fall may alter preconditioning of the water column with regards to the following winter convection.…”

Section: Introductionmentioning

confidence: 99%

Dense shelf water production in the Adélie Depression, East Antarctica, 2004–2012: Impact of the Mertz Glacier calving

et al. 2014

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Summer repeated hydrographic surveys and 4 years of mooring observations are used to characterize for the first time the interannual variability of the bottom water in the Mertz Glacier Polynya (MGP) on the East Antarctic shelf (142 E-146 E). Until 2010, large interannual variability was observed in the summer bottom salinity with year-to-year changes reaching 0.12 in Commonwealth Bay, the region with the highest sea ice production. The summer variability was shown to be linked to the efficiency of the convection during the preceding winter. The recent freshening of the bottom waters subsequent to the Mertz Glacier calving was well beyond the range of the precalving interannual variability. Within 2 years after the event, the bottom water of the shelf became too light to possibly contribute to renewal of the Antarctic Bottom Water. Rough estimates of the freshwater budget of the Ad elie Depression indicate that the freshening necessary to compensate for net sea ice production in the MGP did not change drastically after the Mertz calving. The year-to-year salinity changes appeared to respond to the MGP activity. Yet, prior to the calving, the convective system in the polynya was also partly controlled by the late winter bottom salinity through a mechanism leading to a sequence of alternatively fresher and more saline bottom waters over the period [2007][2008][2009][2010]. Exceptional events like the Mertz calving seem to be able to switch over the system into a less stratified state where convection responds more directly to changes in the surface forcing. IntroductionAntarctic Bottom Water (AABW), the densest water mass of the world ocean, occupies the abyssal layer of the Southern Ocean as a relatively well-oxygenated, cold and fresh product, which spreads north into the Atlantic, Indian, and Pacific oceans. Surface water transformation on the continental margins around Antarctica and subsequent sinking of the dense shelf waters along the slope supply the bottom limb of the ocean thermohaline circulation. It has been argued that changes in the properties or formation rate of the AABW could affect the strength of the thermohaline circulation, and therefore the global climate [Stouffer et al., 2007;Purkey and Johnson, 2012].The production of AABW is considered to originate on the Antarctic shelf in coastal polynyas where nearfreezing water (the so-called High-Salinity Shelf Water, HSSW) is formed through ocean surface cooling and brine drainage from growing sea ice. Upon mixing with ambient waters on the shelf and subsequent sinking and entrainment of Circumpolar Deep Water down the continental slope, these waters eventually acquire final AABW properties when reaching the abyssal layer of the Southern Ocean. While this process is suspected to occur at many locations around Antarctica, observations have unambiguously identified some primary formation sites: the Weddell Sea, the Ross Sea [Carmack, 1977], and the Ad elie-George V Land [Gordon and Tchernia, 1972;Rintoul, 1998]. Estimates of the relative im...

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“…For more details on the study area and the oceanography we refer to numerous papers on the region (e.g. Beaman and Harris, 2005;Cougnon et al, 2013Cougnon et al, , 2017Shadwick et al, 2013;Kusahara et al, 2017;Jansen et al, 2018).…”

Section: Study Areamentioning

confidence: 99%

“…The calving of the Mertz Glacier Tongue (MGT) in 2010 (Young et al, 2010) has resulted in profound environmental changes in the region, such as increased sea-ice concentrations (Campagne et al, 2015), and changes in ocean currents along the shelf as suggested by observations and modeling studies (Cougnon et al, 2017;Kusahara et al, 2017). These environmental changes have consequences for the dynamics and distribution of primary production (Shadwick et al, 2013), the abundance of top-predators (Wilson et al, 2016), and has been observed to influence the community structure of shallow-water benthos (Clark et al, 2015). However, the effect of the MGT-calving on the seafloor across the region has so far neither been assessed nor observed, and so its impact on benthic communities across the continental shelf is still unknown.…”

Section: Introductionmentioning

confidence: 99%

Mapping Antarctic Suspension Feeder Abundances and Seafloor Food-Availability, and Modeling Their Change After a Major Glacier Calving

et al. 2018

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Seafloor communities are a critical part of the unique and diverse Antarctic marine life. Processes at the ocean-surface can strongly influence the diversity and abundance of these communities, even when they live at hundreds of meters water depth. However, even though we understand the importance of this link, there are so far no quantitative spatial predictions on how seafloor communities will respond to changing conditions at the ocean surface. Here, we map patterns in abundance of important habitat-forming suspension feeders on the seafloor in East Antarctica, and predict how these patterns change after a major disturbance in the icescape, caused by the calving of the Mertz Glacier Tongue. We use a purpose-built ocean model for the time-period before and after the calving of the Mertz-Glacier Tongue in 2010, data from satellites and a validated food-availability model to estimate changes in horizontal flux of food since the glacier calving. We then predict the post-calving distribution of suspension feeder abundances using the established relationships with the environmental variables, and changes in horizontal flux of food. Our resulting maps indicate strong increases in suspension feeder abundances close to the glacier calving site, fueled by increased food supply, while the remainder of the region maintains similar suspension feeder abundances despite a slight decrease in total food supply. The oceanographic setting of the entire region changes, with a shorter ice-free season, altered seafloor currents and changes in food-availability. Our study provides important insight into the flow-on effects of a changing icescape on seafloor habitat and fauna in polar environments. Understanding these connections is important in the context of current and future effects of climate change, and the mapped predictions of the seafloor fauna as presented for the study region can be used as a decision-tool for planning potential marine protected areas, and for focusing future sampling and monitoring initiatives.

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Glacier tongue calving reduced dense water formation and enhanced carbon uptake

Cited by 83 publications

References 48 publications

Two decades of inorganic carbon dynamics along the West Antarctic Peninsula

Two decades of inorganic carbon dynamics along the West Antarctic Peninsula

Dense shelf water production in the Adélie Depression, East Antarctica, 2004–2012: Impact of the Mertz Glacier calving

Mapping Antarctic Suspension Feeder Abundances and Seafloor Food-Availability, and Modeling Their Change After a Major Glacier Calving

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