scholarly journals Variability in summer surface residence time within a West Antarctic Peninsula biological hotspot

2018 ◽  
Vol 376 (2122) ◽  
pp. 20170165 ◽  
Author(s):  
Josh T. Kohut ◽  
Peter Winsor ◽  
Hank Statscewich ◽  
Matthew J. Oliver ◽  
Erick Fredj ◽  
...  
Keyword(s):  
Residence Time ◽  
Antarctic Peninsula ◽  
Phytoplankton Biomass ◽  
Antarctic Krill ◽  
Prey Availability ◽  
Rapid Change ◽  
Negative Relationship ◽  
Phytoplankton Productivity ◽  
West Antarctic ◽  
West Antarctic Peninsula

Palmer Deep canyon along the central West Antarctic Peninsula is known to have higher phytoplankton biomass than the surrounding non-canyon regions, but the circulation mechanisms that transport and locally concentrate phytoplankton and Antarctic krill, potentially increasing prey availability to upper-trophic-level predators such as penguins and cetaceans, are currently unknown. We deployed a three-site high-frequency radar network that provided hourly surface circulation maps over the Palmer Deep hotspot. A series of particle release experiments were used to estimate surface residence time and connectivity across the canyon. The majority of residence times fell between 1.0 and 3.5 days, with a mean of 2 days and a maximum of 5 days. We found a highly significant negative relationship between wind speed and residence time. Our residence time analysis indicates that the elevated phytoplankton biomass over the central canyon is transported into and out of the hotspot on time scales much shorter than the observed phytoplankton growth rate, suggesting that the canyon may not act as an incubator of phytoplankton productivity as previously suggested. It may instead serve more as a conveyor belt of phytoplankton biomass produced elsewhere, continually replenishing the phytoplankton biomass for the local Antarctic krill community, which in turn supports numerous top predators. This article is part of the theme issue ‘The marine system of the West Antarctic Peninsula: status and strategy for progress in a region of rapid change’.

scholarly journals Changes in the upper ocean mixed layer and phytoplankton productivity along the West Antarctic Peninsula

2018 ◽  
Vol 376 (2122) ◽  
pp. 20170173 ◽  
Author(s):  
Oscar Schofield ◽  
Michael Brown ◽  
Josh Kohut ◽  
Schuyler Nardelli ◽  
Grace Saba ◽  
...  
Keyword(s):  
Sea Ice ◽  
Antarctic Peninsula ◽  
Mixed Layer ◽  
Carbon Fixation ◽  
Upper Ocean ◽  
The West ◽  
Phytoplankton Productivity ◽  
West Antarctic ◽  
West Antarctic Peninsula

The West Antarctic Peninsula (WAP) has experienced significant change over the last 50 years. Using a 24 year spatial time series collected by the Palmer Long Term Ecological Research programme, we assessed long-term patterns in the sea ice, upper mixed layer depth (MLD) and phytoplankton productivity. The number of sea ice days steadily declined from the 1980s until a recent reversal that began in 2008. Results show regional differences between the northern and southern regions sampled during regional ship surveys conducted each austral summer. In the southern WAP, upper ocean MLD has shallowed by a factor of 2. Associated with the shallower mixed layer is enhanced phytoplankton carbon fixation. In the north, significant interannual variability resulted in the mixed layer showing no trended change over time and there was no significant increase in the phytoplankton productivity. Associated with the recent increases in sea ice there has been an increase in the photosynthetic efficiency (chlorophyll a -normalized carbon fixation) in the northern and southern regions of the WAP. We hypothesize the increase in sea ice results in increased micronutrient delivery to the continental shelf which in turn leads to enhanced photosynthetic performance. This article is part of the theme issue ‘The marine system of the West Antarctic Peninsula: status and strategy for progress in a region of rapid change’.

scholarly journals Macronutrient and carbon supply, uptake and cycling across the Antarctic Peninsula shelf during summer

2018 ◽  
Vol 376 (2122) ◽  
pp. 20170168 ◽  
Author(s):  
Sian F. Henley ◽  
Elizabeth M. Jones ◽  
Hugh J. Venables ◽  
Michael P. Meredith ◽  
Yvonne L. Firing ◽  
...  
Keyword(s):  
Antarctic Peninsula ◽  
Inorganic Carbon ◽  
Carbon Sink ◽  
Significant Proportion ◽  
Rapid Change ◽  
The West ◽  
Carbon Supply ◽  
West Antarctic ◽  
Shelf Sediment ◽  
West Antarctic Peninsula

The West Antarctic Peninsula shelf is a region of high seasonal primary production which supports a large and productive food web, where macronutrients and inorganic carbon are sourced primarily from intrusions of warm saline Circumpolar Deep Water. We examined the cross-shelf modification of this water mass during mid-summer 2015 to understand the supply of nutrients and carbon to the productive surface ocean, and their subsequent uptake and cycling. We show that nitrate, phosphate, silicic acid and inorganic carbon are progressively enriched in subsurface waters across the shelf, contrary to cross-shelf reductions in heat, salinity and density. We use nutrient stoichiometric and isotopic approaches to invoke remineralization of organic matter, including nitrification below the euphotic surface layer, and dissolution of biogenic silica in deeper waters and potentially shelf sediment porewaters, as the primary drivers of cross-shelf enrichments. Regenerated nitrate and phosphate account for a significant proportion of the total pools of these nutrients in the upper ocean, with implications for the seasonal carbon sink. Understanding nutrient and carbon dynamics in this region now will inform predictions of future biogeochemical changes in the context of substantial variability and ongoing changes in the physical environment. This article is part of the theme issue ‘The marine system of the West Antarctic Peninsula: status and strategy for progress in a region of rapid change’.

scholarly journals A ‘shallow bathtub ring’ of local sedimentary iron input maintains the Palmer Deep biological hotspot on the West Antarctic Peninsula shelf

2018 ◽  
Vol 376 (2122) ◽  
pp. 20170171 ◽  
Author(s):  
Robert M. Sherrell ◽  
Amber L. Annett ◽  
Jessica N. Fitzsimmons ◽  
Vincent J. Roccanova ◽  
Michael P. Meredith
Keyword(s):  
Antarctic Peninsula ◽  
Deep Water ◽  
Rapid Change ◽  
Euphotic Zone ◽  
The West ◽  
Inner Shelf ◽  
West Antarctic ◽  
Limiting Nutrient ◽  
Marine System ◽  
West Antarctic Peninsula

Palmer Deep (PD) is one of several regional hotspots of biological productivity along the inner shelf of the West Antarctic Peninsula. The proximity of hotspots to shelf-crossing deep troughs has led to the ‘canyon hypothesis’, which proposes that circumpolar deep water flowing shoreward along the canyons is upwelled on the inner shelf, carrying nutrients including iron (Fe) to surface waters, maintaining phytoplankton blooms. We present here full-depth profiles of dissolved and particulate Fe and manganese (Mn) from eight stations around PD, sampled in January and early February of 2015 and 2016, allowing the first detailed evaluation of Fe sources to the area's euphotic zone. We show that upwelling of deep water does not control Fe flux to the surface; instead, shallow sediment-sourced Fe inputs are transported horizontally from surrounding coastlines, creating strong vertical gradients of dissolved Fe within the upper 100 m that supply this limiting nutrient to the local ecosystem. The supply of bioavailable Fe is, therefore, not significantly related to the canyon transport of deep water. Near shore time-series samples reveal that local glacial meltwater appears to be an important Mn source but, surprisingly, is not a large direct Fe input to this biological hotspot. This article is part of the theme issue ‘The marine system of the West Antarctic Peninsula: status and strategy for progress in a region of rapid change’.

scholarly journals Evidences of strong sources of DFe and DMn in Ryder Bay, Western Antarctic Peninsula

2018 ◽  
Vol 376 (2122) ◽  
pp. 20170172 ◽  
Author(s):  
Johann Bown ◽  
Hans van Haren ◽  
Michael P. Meredith ◽  
Hugh J. Venables ◽  
Patrick Laan ◽  
...  
Keyword(s):  
Antarctic Peninsula ◽  
Sediment Resuspension ◽  
Vertical Mixing ◽  
Rapid Change ◽  
Austral Summer ◽  
Bottom Surface ◽  
The West ◽  
West Antarctic ◽  
Deep Waters ◽  
West Antarctic Peninsula

The spatial distribution, biogeochemical cycling and external sources of dissolved iron and dissolved manganese (DFe and DMn) were investigated in Ryder Bay, a small coastal embayment of the West Antarctic Peninsula, during Austral summer (2013 and 2014). Dissolved concentrations were measured throughout the water column at 11 stations within Ryder Bay. The concentration ranges of DFe and DMn were large, between 0.58 and 32.7 nM, and between 0.18 and 26.2 nM, respectively, exhibiting strong gradients from the surface to the bottom. Surface concentrations of DFe and DMn were higher than concentrations reported for the Southern Ocean and coastal Antarctic waters, and extremely high concentrations were detected in deep water. Glacial meltwater and shallow sediments are likely to be the main sources of DFe and DMn in the euphotic zone, while lateral advection associated with local sediment resuspension and vertical mixing are significant sources for intermediate and deep waters. During summer, vertical mixing of intermediate and deep waters and sediment resuspension occurring from Marguerite Trough to Ryder Bay are thought to be amplified by a series of overflows at the sills, enhancing the input of Fe and Mn from bottom sediment and increasing their concentrations up to the euphotic layer. This article is part of the theme issue ‘The marine system of the West Antarctic Peninsula: status and strategy for progress in a region of rapid change’.

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