Multiplatform, Multidisciplinary Investigations of the Impacts of Modified Circumpolar Deep Water in the Ross Sea, Antarctica

Smith, Walker O; Goetz, Kimberly T.; Kaufman, Daniel E.; Queste, Bastien Y.; Asper, Vernon; Costa, Daniel P.; Dinniman, Michael S.; Friedrichs, Marjorie A. M.; Hofmann, Eileen E.; Heywood, Karen J.; Klinck, John M.; Kohut, Josh; Lee, Craig M.

doi:10.5670/oceanog.2014.36

Cited by 8 publications

(5 citation statements)

References 15 publications

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“…This work underscores the need for improved and coordinated in situ time series observations of air-ocean-ice interactions, coupled with continued improvements in satellite-derived products and high-resolution ocean models. Although acquiring in situ observations is challenging, given the highly dynamic nature of Antarctic sea ice, newer, cost-effective and more sophisticated technologies (e.g., autonomous vehicles and moored instrumentation) are now making such observations possible (Schofield et al, 2010(Schofield et al, , 2015Maksym et al, 2012;Smith et al, 2014;Ackley et al, 2015;Ducklow et al, 2015). By joining these efforts, we will better resolve cause and effect and better assess future changes to this highly sensitive and rapidly changing marine environment.…”

Section: Discussionmentioning

confidence: 99%

Seasonal sea ice changes in the Amundsen Sea, Antarctica, over the period of 1979–2014

Stammerjohn

Maksym

Massom

et al. 2015

Elementa: Science of the Anthropocene

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Recent attention has focused on accelerated glacial losses along the Amundsen Sea coast that result from changes in atmosphere and ocean circulation, with sea ice playing a mediating but not well-understood role. Here, we investigated how sea ice has changed in the Amundsen Sea over the period of 1979 to 2014, focusing on spatio-temporal changes in ice edge advance/retreat and percent sea ice cover in relation to changes in winds. In contrast to the widespread sea ice decreases to the east and increases to the west of the Amundsen Sea, sea ice changes in the Amundsen Sea were confined to three areas: (i) offshore of the shelf break, (ii) the southern Pine Island Polynya, and (iii) the eastern Amundsen Sea Polynya. Offshore, a 2-month decrease in ice season duration coincided with seasonal shifts in wind speed and direction from March to May (relating to later ice advance) and from September to August (relating to earlier retreat), consistent with reported changes in the depth/location of the Amundsen Sea Low. In contrast, sea ice decreases in the polynya areas corresponded to episodic or step changes in spring ice retreat (earlier by 1-2 months) and were coincident with changes to Thwaites Iceberg Tongue (located between the two polynyas) and increased southeasterly winds. Temporal correlations among these three areas were weak, indicating different local forcing and/or differential response to large-scale forcing. Although our analysis has shown that part of the variability can be explained by changes in winds or to the coastal icescape, an additional but unknown factor is how sea ice has responded to changes in ocean heat and freshwater inputs. Unraveling cause and effect, critical for predicting changes to this rapidly evolving ocean-ice shelf-sea ice system, will require in situ observations, along with improved remote sensing capabilities and ocean modeling.

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Section: Discussionmentioning

confidence: 99%

Seasonal sea ice changes in the Amundsen Sea, Antarctica, over the period of 1979–2014

Stammerjohn

Maksym

Massom

et al. 2015

Elementa: Science of the Anthropocene

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“…Environmental conditions are critical in determining how the composition and dynamics of the phytoplankton vary throughout the growing season. Observations from an autonomous glider in 2010–2011 [ Smith et al ., ] suggested that a transition of the phytoplankton assemblage from P. antarctica to diatoms was associated with a change in the ratio of carbon to chlorophyll [ Kaufman et al ., ]. Analysis of the oceanographic conditions showed this change to be most highly correlated with temperature; however, it was not clear whether the correlation represented a causal relationship or a coincident seasonal trend.…”

Section: Introductionmentioning

confidence: 99%

Climate change impacts on southern Ross Sea phytoplankton composition, productivity, and export

et al. 2017

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The Ross Sea, a highly productive region of the Southern Ocean, is expected to experience warming during the next century along with reduced summer sea ice concentrations and shallower mixed layers. This study investigates how these climatic changes may alter phytoplankton assemblage composition, primary productivity, and export. Glider measurements are used to force a one‐dimensional biogeochemical model, which includes diatoms and both solitary and colonial forms of Phaeocystis antarctica. Model performance is evaluated with glider observations, and experiments are conducted using projections of physical drivers for mid‐21st and late‐21st century. These scenarios reveal a 5% increase in primary productivity by midcentury and 14% by late‐century and a proportional increase in carbon export, which remains approximately 18% of primary production. In addition, scenario results indicate diatom biomass increases while P. antarctica biomass decreases in the first half of the 21st century. In the second half of the century, diatom biomass remains relatively constant and P. antarctica biomass increases. Additional scenarios examining the independent contributions of expected future changes (temperature, mixed layer depth, irradiance, and surface iron inputs from melting ice) demonstrate that earlier availability of low light due to reduction of sea ice early in the growing season is the primary driver of productivity increases over the next century; shallower mixed layer depths additionally contribute to changes of assemblage composition and export. This study further demonstrates how glider data can be effectively used to facilitate model development and simulation, and inform interpretation of biogeochemical observations in the context of climate change.

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“…Cruise transects across the continental shelf show a marked spatial variability in both the east-west and north-south direction over short periods of time (Smith et al, 2013). Within the Ross Sea polynya, ship-based observations show biochemical gradients that suggest patchiness of phytoplankton dynamics on the mesoscale (Hales and Takahashi, 2004;Smith et al, 2017). Nutrient pools have been found to exhibit gradients from both north to south and east to west (DiTullio and Smith, 1996;Sedwick et al, 2011;Smith et al, 2013;Marsay et al, 2014), and phytoplankton assemblage composition is not necessarily uniform across longitudes (DiTullio and Smith, 1996;Garrison et al, 2003;Smith et al, 2013).…”

Section: Spatial Variation Within the Glider Trackmentioning

confidence: 99%

In response to the helpful comments of M.E. Gharamti, we have clarified aspects of the methodology and improved the readability.

Kaufman¹

2017

Preprint

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The Ross Sea is a region characterized by high primary productivity in comparison to other Antarctic coastal regions, and its productivity is marked by considerable variability both spatially (1-50 km) and temporally (days to weeks). This variability presents a challenge for inferring phytoplankton dynamics from observations that are limited in time or space, which is often the case due to logistical limitations of sampling. To better understand the spatiotemporal variability in Ross Sea phytoplankton dynamics and to determine how restricted sampling may skew dynamical interpretations, high-resolution bio-optical glider measurements were assimilated into a one-dimensional biogeochemical model adapted for the Ross Sea. The assimilation of data from the entire glider track using the micro-genetic and local search algorithms in the Marine Model Optimization Testbed improves the model-data fit by ∼ 50 %, generating rates of integrated primary production of 104 g C m −2 yr −1 and export at 200 m of 27 g C m −2 yr −1. Assimilating glider data from three different latitudinal bands and three different longitudinal bands results in minimal changes to the simulations, improves the model-data fit with respect to unassimilated data by ∼ 35 %, and confirms that analyzing these glider observations as a time series via a one-dimensional model is reasonable on these scales. Whereas assimilating the full glider data set produces well-constrained simulations, assimilating subsampled glider data at a frequency consistent with cruise-based sampling results in a wide range of primary production and export estimates. These estimates depend strongly on the timing of the assimilated observations, due to the presence of high mesoscale variability in this region. Assimilating surface glider data subsampled at a frequency consistent with available satellite-derived data results in 40 % lower carbon export, primarily resulting from optimized rates generating more slowly sinking diatoms. This analysis highlights the need for the strategic consideration of the impacts of data frequency, duration, and coverage when combining observations with biogeochemical modeling in regions with strong mesoscale variability.

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Multiplatform, Multidisciplinary Investigations of the Impacts of Modified Circumpolar Deep Water in the Ross Sea, Antarctica

Cited by 8 publications

References 15 publications

Seasonal sea ice changes in the Amundsen Sea, Antarctica, over the period of 1979–2014

Seasonal sea ice changes in the Amundsen Sea, Antarctica, over the period of 1979–2014

Climate change impacts on southern Ross Sea phytoplankton composition, productivity, and export

In response to the helpful comments of M.E. Gharamti, we have clarified aspects of the methodology and improved the readability.

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