Spatial analysis of trends in primary production and relationship with large‐scale climate variability in the <scp>R</scp>oss <scp>S</scp>ea, <scp>A</scp>ntarctica (1997–2013)

O’Connell-Milne

Limnology & Oceanography

et al. 2019

The dynamics of freeze and thaw events in Antarctic sea ice impart chemical changes in the underlying sea water. Trace metals in sea ice and accumulated through deposition of dust are released into sea water as sea ice breaks up in spring. Clams such as Laternula elliptica incorporate a record of these and associated chemical dynamics in their carbonate shells. In 2012, we collected samples of L. elliptica from three sites along a sea ice persistence gradient in McMurdo Sound, Ross Sea Antarctica. Concentrations of trace metals in the chondrophore of each shell were measured by laser ablation inductively coupled plasma mass spectrometry. Ablations transected annual growth increments creating time series ranging in length from 13 to 25 yr. An 8‐yr time period of persistent sea ice, associated with presence of the B‐15 and C‐19 icebergs at the entrance of McMurdo Sound, was clearly resolved in the trace element time series. Conservative trace metals (Sr, Ba) were found at higher concentrations, and highly scavenged elements (Pb, Cu) were found at lower concentrations at sites with more persistent sea ice and during the 8‐yr period of iceberg‐influenced sea ice persistence. Bioactive trace metals (Fe, Ni) were found in higher concentrations during ice free conditions, associated with a period of high pelagic productivity. Our results provide an important case study for understanding the chemical signature of changing sea ice dynamics as reflected in bivalve shell material under a changing Antarctic climate.

Section: Discussionsupporting

confidence: 92%

Trace metals in Antarctic clam shells record the chemical dynamics of changing sea ice conditions

O’Connell-Milne

Limnology & Oceanography

et al. 2019

“…Along with climatic change in temperatures, sea ice and vertical mixing are changing in the Ross Sea. Average sea ice extent and duration have in general been increasing throughout the Ross Sea since at least the 1990s [ Comiso and Nishio , ; Cavalieri and Parkinson , ; Stammerjohn et al ., ; Sinclair et al ., ], but within the Ross Sea polynya there have also been slight increases in the number of ice‐free days between 1992 and 2013 [ Schine et al ., ]. A marked freshening of the Ross Sea has been observed since the midtwentieth century, increasing the buoyancy of surface waters and likely diminishing vertical exchange [ Jacobs et al ., ; Jacobs and Giulivi , ].…”

Section: Introductionmentioning

confidence: 99%

“…A marked freshening of the Ross Sea has been observed since the midtwentieth century, increasing the buoyancy of surface waters and likely diminishing vertical exchange [ Jacobs et al ., ; Jacobs and Giulivi , ]. Additionally, the timing and magnitude of primary productivity in the Ross Sea have been changing over the past two decades [ Arrigo et al ., ; Montes‐Hugo and Yuan , ; Schine et al ., ]. Between 1997 and 2013, trends in annual net primary production have been correlated with the number of ice‐free days and have been generally increasing in the area of the Ross Sea polynya, but decreasing to the east and northwest [ Schine et al ., ].…”

Section: Introductionmentioning

confidence: 99%

“…Additionally, the timing and magnitude of primary productivity in the Ross Sea have been changing over the past two decades [ Arrigo et al ., ; Montes‐Hugo and Yuan , ; Schine et al ., ]. Between 1997 and 2013, trends in annual net primary production have been correlated with the number of ice‐free days and have been generally increasing in the area of the Ross Sea polynya, but decreasing to the east and northwest [ Schine et al ., ].…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

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

et al. 2017

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.

“…Typically, sampling stations are separated by tens of kilometers (Hales and Takahashi, 2004), and although vessels may return to resample a station, they typically do not return more than once or twice in a single year. During the 1990s, the use of remote sensing was expanded to look more closely at the Ross Sea bloom (Arrigo and McClain, 1994), and satellite retrievals have continued to provide valuable insights into characteristics of the phytoplankton assemblage (Arrigo et al, 1998;Arrigo and van Dijken, 2004;Peloquin and Smith, 2007;Schine et al, 2015). Satellite observations offer a synoptic view of spatial regions at frequencies that are within the timescale of biological changes (e.g., growth); however, the presence of sea ice and clouds often obscures remote-sensing measurements in the Ross Sea (Arrigo et al, 1998).…”

Section: Introductionmentioning

confidence: 99%

Assimilating bio-optical glider data during a phytoplankton bloom in the southern Ross Sea

Kaufman¹,

Friedrichs²,

Hemmings³

et al. 2018

Biogeosciences

Abstract. 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.