Sea Ice Meltwater and Circumpolar Deep Water Drive Contrasting Productivity in Three Antarctic Polynyas

Moreau, Sébastien; Lannuzel, Delphine; Janssens, Julie; Arroyo, Mar C.; Corkill, Matthew; Cougnon, Eva A.; Genovese, Cristina; Legrésy, B.; Lenton, Andrew; Puigcorbé, Viena; Ratnarajah, Lavenia; Rintoul, Stephen R.; Roca‐Martí, Montserrat; Rosenberg, Mark; Shadwick, Elizabeth H.; Silvano, Alessandro; Strutton, Peter G.; Tilbrook, Bronte

doi:10.1029/2019jc015071

Cited by 39 publications

(49 citation statements)

References 105 publications

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“…Journal of Geophysical Research: Oceans East Antarctica (Moreau et al, 2019). Correspondingly, the relative importance of the different dFe sources obtained from this simulation shows regional variability.…”

Section: 1029/2019jc015736mentioning

confidence: 64%

Analysis of Iron Sources in Antarctic Continental Shelf Waters

et al. 2020

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Previous studies showed that satellite-derived estimates of chlorophyll a in coastal polynyas over the Antarctic continental shelf are correlated with the basal melt rate of adjacent ice shelves. A 5-km resolution ocean/sea ice/ice shelf model of the Southern Ocean is used to examine mechanisms that supply the limiting micronutrient iron to Antarctic continental shelf surface waters. Four sources of dissolved iron are simulated with independent tracers, assumptions about the source iron concentration for each tracer, and an idealized summer biological uptake. Iron from ice shelf melt provides about 6% of the total dissolved iron in surface waters. The contribution from deep sources of iron on the shelf (sediments and Circumpolar Deep Water) is much larger at 71%. The relative contribution of dissolved iron supply from basal melt driven overturning circulation within ice shelf cavities is heterogeneous around Antarctica, but at some locations, such as the Amundsen Sea, it is the primary mechanism for transporting deep dissolved iron to the surface. Correlations between satellite chlorophyll a in coastal polynyas around Antarctica and simulated dissolved iron confirm the previous suggestion that productivity of the polynyas is linked to the basal melt of adjacent ice shelves. This correlation is the result of upward advection or mixing of iron-rich deep waters due to circulation changes driven by ice shelf melt, rather than a direct influence of iron released from melting ice shelves. This dependence highlights the potential vulnerability of coastal Antarctic ecosystems to changes in ice shelf basal melt rates. Plain Language Summary Phytoplankton in Antarctic coastal waters grow more rapidly relative to waters farther offshore. This growth is limited by the availability of light for photosynthesis and the supply of the micronutrient dissolved iron. Earlier studies suggest that satellite-based estimates of phytoplankton growth are related to the melting of nearby floating portions (called ice shelves) of the Antarctic ice sheet. In this study, a computer model, which includes melting of ice shelves, is used to examine the different sources of dissolved iron that supply the well-lit summer surface waters around Antarctica. Dissolved iron is available in the floating ice shelves, and the direct supply of this iron to coastal waters by melting of the bottom of the ice shelf is important for enhancing biological production. However, melting creates less dense water at the ice shelf base that rises and brings deep waters that contain dissolved iron towards the surface in front of the ice shelf. The model shows that this input provides a larger source of dissolved iron to the open surface waters in many coastal regions than does direct supply from the ice shelf meltwater. This implies that phytoplankton growth may be vulnerable to changes in ice shelf basal melt.

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Section: 1029/2019jc015736mentioning

confidence: 64%

Analysis of Iron Sources in Antarctic Continental Shelf Waters

et al. 2020

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“…These corresponding impacts to the CO 2 system have been primarily attributed to an enhancement in biological production as a result of large increases in sea ice meltwater, potentially delivering a source of dissolved iron to the mixed layers (Shadwick et al, ). A recent analysis by Moreau et al () concluded that a larger volume of sea ice meltwater in the Mertz Polynya and neighboring Ninnis Polynya best explained their enhanced biological productivities relative to the Dalton Polynya. The calving of the MGT in the Mertz Polynya set up an interesting natural experiment to assess how changes to the Antarctic icescape impact polynya productivity.…”

Section: Discussionmentioning

confidence: 99%

“…In the Terra Nova Bay (TNB) polynya in the western Ross Sea (163–167°E), late summer NCP is an order of magnitude larger than the Dalton polynya at roughly 425 mmol C m −2 day −1 (Table ; DeJong et al, ). Biological production in TNB is typically dominated by diatoms in summer when stratification is stronger and mixed layers are shallower (Arrigo et al, ; Tortell et al, ), in contrast to the Phaeocystis antarctica communities in the Dalton Polynya (Moreau et al, ). Polynya formation in TNB is primarily driven by intense offshore katabatic winds (Bromwich & Kurtz, ) that prevent a consolidated sea ice pack from forming in the lee of the Drygalski Ice Tongue, with wind speeds often ranging between 10 and 30 m/s (Bromwich, ).…”

Section: Discussionmentioning

confidence: 99%

Summer Carbonate Chemistry in the Dalton Polynya, East Antarctica

Arroyo¹,

Shadwick

Tilbrook

2019

JGR Oceans

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The carbonate chemistry in the Dalton Polynya in East Antarctica (115°–123°E) was investigated in summer 2014/2015 using high‐frequency underway measurements of CO2 fugacity (fCO2) and discrete water column measurements of total dissolved inorganic carbon (TCO2) and total alkalinity. Air‐sea CO2 fluxes indicate this region was a weak net source of CO2 to the atmosphere (0.7 ± 0.9 mmol C m−2 day−1) during the period of observation, with the largest degree of surface water supersaturation (ΔfCO2 = +45 μatm) in ice‐covered waters near the Totten Ice Shelf (TIS) as compared to the ice‐free surface waters in the Dalton Polynya. The seasonal depletion of mixed‐layer TCO2 (6 to 51 μmol/kg) in ice‐free regions was primarily driven by sea ice melt and biological CO2 uptake. Estimates of net community production (NCP) reveal net autotrophy in the ice‐free Dalton Polynya (NCP = 5–20 mmol C m−2 day−1) and weakly heterotrophic waters near the ice‐covered TIS (NCP = −4–0 mmol C m−2 day−1). Satellite‐derived estimates of chlorophyll a (Chl a) and sea ice coverage suggest that the early summer season in 2014/2015 was anomalous relative to the long‐term (1997–2017) record, with lower surface Chl a concentrations and a greater degree of sea ice cover during the period of observation; the implications for seasonal primary production and air‐sea CO2 exchange are discussed. This study highlights the importance of both physical and biological processes in controlling air‐sea CO2 fluxes and the significant interannual variability of the CO2 system in Antarctic coastal regions.

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“…Polynyas are areas where particle fluxes are expected to be significant, and they also harbor high densities of upper trophic level organisms such as birds and marine mammals (Karnovsky et al, 2007). Further information regarding the sampling area can be found in Moreau et al (2019). Samples were collected at two mesopelagic depths (100 and 300 m), using either a 12L-Niskin bottle (BTL-samples) or an in situ pump (ISP-samples) deployed at each depth.…”

Section: Study Areamentioning

confidence: 99%

Sampling Device-Dependence of Prokaryotic Community Structure on Marine Particles: Higher Diversity Recovered by in situ Pumps Than by Oceanographic Bottles

et al. 2020

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Microbes associated with sinking marine particles play key roles in carbon sequestration in the ocean. The sampling of particle-attached microorganisms is often done with sediment traps or by filtration of water collected with oceanographic bottles, both involving a certain time lapse between collection and processing of samples that may result in changes in particle-attached microbial communities. Conversely, in situ water filtration through submersible pumps allows a faster storage of sampled particles, but it has rarely been used to study the associated microbial communities and has never been compared to other particle-sampling methods in terms of the recovery of particle microbial diversity. Here we compared the prokaryotic communities attached to small (1-53 µm) and large (>53 µm) particles collected from the mesopelagic zone (100-300 m) of two Antarctic polynyas using in situ pumps (ISP) and oceanographic bottles (BTL). Each sampling method retrieved largely different particle-attached communities, suggesting that they capture different kinds of particles. These device-driven differences were greater for large particles than for small particles. Overall, the ISP recovered 1.5to 3-fold more particle-attached bacterial taxa than the BTL, and different taxonomic groups were preferentially recovered by each method. In particular, typical particleattached groups such as Planctomycetes and Deltaproteobacteria recovered with ISP were nearly absent from BTL samples. Our results suggest that the method used to sample marine particles has a strong influence in our view of their associated microbial communities.

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Sea Ice Meltwater and Circumpolar Deep Water Drive Contrasting Productivity in Three Antarctic Polynyas

Cited by 39 publications

References 105 publications

Analysis of Iron Sources in Antarctic Continental Shelf Waters

Analysis of Iron Sources in Antarctic Continental Shelf Waters

Summer Carbonate Chemistry in the Dalton Polynya, East Antarctica

Sampling Device-Dependence of Prokaryotic Community Structure on Marine Particles: Higher Diversity Recovered by in situ Pumps Than by Oceanographic Bottles

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