An anticyclonic circulation above the Northwest Georgia Rise, Southern Ocean

Meredith, Michael P.; Watkins, J. L.; Murphy, Eugene J.; Cunningham, Nathan; Wood, Andrew G.; Korb, Rebecca E.; Whitehouse, M. J.; Thorpe, Sally; Vivier, Frédéric

doi:10.1029/2003gl018039

Cited by 67 publications

(69 citation statements)

References 16 publications

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“…At P3, the sediment trap deployment location is positioned in the center of a cyclonic circulation feature originating from the northern South Georgia shelf (Meredith et al, 2003). The area downstream of South Georgia is fertilized by continuous benthic iron supply from the South Georgia shelf system, resulting in higher dissolved iron concentration when compared to the waters upstream of the island (0.3 nM versus o0.05 nM in spring, Nielsdóttir et al, 2012).…”

Section: Magnitude Of Particle Fluxesmentioning

confidence: 99%

“…To describe the change in diatom assemblage with depth, we compared the annual sediment trap record from P3 with mixed layer diatom assemblage from multiple summer surveys (February 2002, 2003and January 2005 at the P3 trap location (Korb et al, 2008) and surface sediment diatom assemblage from a core located very close to the trap (42°09.2′S-41°10.7′W, 3760 m, Allen et al, 2005).…”

Section: Diatom Enumeration Identification and Biomassmentioning

confidence: 99%

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Strong contribution of diatom resting spores to deep-sea carbon transfer in naturally iron-fertilized waters downstream of South Georgia

Rembauville

Manno

Tarling

et al. 2016

Deep Sea Research Part I: Oceanographic Research Papers

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a b s t r a c tBiogeochemical and diatom export fluxes are presented from two bathypelagic sediment trap deployments in the Antarctic Zone of the Southern Ocean. One of the sediment traps was deployed in very productive, naturally iron-fertilized waters downstream of South Georgia (P3, 2000 m) and compared to a deployment in moderately productive waters upstream of the island system (P2, 1500 m). At both sites significant diatom export events occurred in spring (November) and contained mostly empty cells that were associated with low particulate organic carbon (POC) fluxes. A summer export pulse occurred one month later at P2 (end February/March) compared to P3 (end January). Diatom fluxes at P3 were one order of magnitude higher than at P2, a difference mainly attributed to the short and intense export of resting spores from Chaetoceros Hyalochaete and Thalassiosira antarctica species. Aside from these resting spores, diatom export assemblages at both sites were dominated by empty Fragilariopsis kerguelensis frustules. The fraction of diatoms exported as empty frustules was considerably lower at P3 (52%) than P2 (91%). This difference was related to the flux of intact diatom resting spores at P3 and may partially explain the lower Si:C export stoichiometry observed at P3 (1.1) compared to P2 (1.5). Through the enumeration of full diatom frustules and subsequent biomass calculations we estimate that diatom resting spores account for 42% of annual POC flux in the productive waters downstream of South Georgia. At both sites the contribution of diatom vegetative stages to POC fluxes was considerably lower (o 5%). From these analyses we conclude that resting spore export contributes towards the slightly higher bathypelagic (POC) flux at P3 (40.6 mmol m À 2 y À 1 ) compared to P2 (26.4 mmol m À 2 y À 1 ). We compared our sediment trap records with previously published diatom assemblage data from the mixed layer and surface sediments (3760 m) around South Georgia. The relative proportion of diatom resting spores within diatom assemblages increases as a function of depth and is explained by selective preservation of their robust frustules. Our study highlights the significance of diatom resting spore export as a carbon vector out of the mixed layer. Furthermore, the contribution or resting spores to POC flux in the bathypelagic ocean and sediments suggests they play a particularly important role in sequestering biologically fixed CO 2 over climatically relevant timescales.

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Section: Magnitude Of Particle Fluxesmentioning

confidence: 99%

Section: Diatom Enumeration Identification and Biomassmentioning

confidence: 99%

Strong contribution of diatom resting spores to deep-sea carbon transfer in naturally iron-fertilized waters downstream of South Georgia

Rembauville

Manno

Tarling

et al. 2016

Deep Sea Research Part I: Oceanographic Research Papers

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“…6b). Closer to the coast where satellite altimetry suffers from inaccuracies and data gaps (Bouffard et al, 2007;Volkov et al, 2007), the validation of modelled surface circulation patterns was integrated using in situ current measurements or surface drifter trajectories presented in previous publications (Whitehouse et al, 2008a;Thorpe et al, 2002;Korb et al, 2008;Meredith et al, 2003).…”

Section: Surface Water Circulationmentioning

confidence: 99%

Sedimentary and atmospheric sources of iron around South Georgia, Southern Ocean: a modelling perspective

et al. 2014

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Abstract. In high-nutrient low-chlorophyll waters of the western Atlantic sector of the Southern Ocean, an intense phytoplankton bloom is observed annually north of South Georgia. Multiple sources, including shallow sediments and atmospheric dust deposition, are thought to introduce iron to the region. However, the relative importance of each source is still unclear, owing in part to the scarcity of dissolved iron (dFe) measurements in the South Georgia region. In this study, we combine results from a recently published dFe data set around South Georgia with a coupled regional hydrodynamic and biogeochemical model to further investigate iron supply around the island. The biogeochemical component of the model includes an iron cycle, where sediments and dust deposition are the sources of iron to the ocean. The model captures the characteristic flow patterns around South Georgia, hence simulating a large phytoplankton bloom to the north (i.e. downstream) of the island. Modelled dFe concentrations agree well with observations (mean difference and root mean square errors of ∼ 0.02 nM and ∼ 0.81 nM) and form a large plume to the north of the island that extends eastwards for more than 800 km. In agreement with observations, highest dFe concentrations are located along the coast and decrease with distance from the island. Sensitivity tests indicate that most of the iron measured in the main bloom area originates from the coast and very shallow shelf-sediments (depths < 20 m). Dust deposition exerts almost no effect on surface chlorophyll a concentrations. Other sources of iron such as run-off and glacial melt are not represented explicitly in the model, however we discuss their role in the local iron budget.

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“…Dashed grey lines indicate possible current paths as derived from model and drifter data (Thorpe et al 2002). Isobaths are shown every 1,000 m et al 2002;Meredith et al 2003). Model and drifter data suggests that waters along the North Scotia Ridge as far west as 45°W may have passed in close proximity to shallow topography on the South Georgia shelf (Thorpe et al 2002).…”

Section: Introductionmentioning

confidence: 99%

Physiological state of phytoplankton communities in the Southwest Atlantic sector of the Southern Ocean, as measured by fast repetition rate fluorometry

et al. 2005

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The majority of the Southern Ocean is a high-nutrient low-chlorophyll (HNLC) ecosystem. Localized increases in chlorophyll concentration measured in the wake of bathymetric features near South Georgia demonstrate variations in the factors governing the HNLC condition. We explore the possibility that the contrast between these areas of high-chlorophyll and surrounding HNLC areas is associated with variations in phytoplankton photophysiology. Total dissolvable iron concentrations, phytoplankton photophysiology and community structure were investigated in late April 2003 on a transect along the North Scotia Ridge (53–54°S) between the Falkland Islands and South Georgia (58–33°W). Total dissolvable iron concentrations suggested a benthic source of iron near South Georgia. Bulk community measurements of dark-adapted photochemical quantum efficiency (F v/F m) exhibited a sharp increase to the east of 46°W coincident with a decrease in the functional absorption cross-section (sPSII). Phytoplankton populations east of 46°W thus displayed no physiological symptoms of iron or nitrate stress. Contrasting low F v/F m west of 46°W could not be explained by variations in the macronutrients nitrate and silicic acid and may be the result of taxon specific variability in photophysiology or iron stress. We hypothesize that increased F v/F m resulted from local relief from iron-stress near South Georgia, east of Aurora Bank, an area previously speculated to be a “pulse point” source of iron. Our measurements provide one of the first direct physiological confirmations that iron stress is alleviated in phytoplankton populations near South Georgia

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An anticyclonic circulation above the Northwest Georgia Rise, Southern Ocean

Cited by 67 publications

References 16 publications

Strong contribution of diatom resting spores to deep-sea carbon transfer in naturally iron-fertilized waters downstream of South Georgia

Strong contribution of diatom resting spores to deep-sea carbon transfer in naturally iron-fertilized waters downstream of South Georgia

Sedimentary and atmospheric sources of iron around South Georgia, Southern Ocean: a modelling perspective

Physiological state of phytoplankton communities in the Southwest Atlantic sector of the Southern Ocean, as measured by fast repetition rate fluorometry

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