Molecular underpinnings and biogeochemical consequences of enhanced diatom growth in a warming Southern Ocean

The Southern Ocean (SO) harbors some of the most intense phytoplankton blooms on Earth. Changes in temperature and iron availability are expected to alter the intensity of SO phytoplankton blooms, but little is known about how these changes will influence community composition and downstream biogeochemical processes. We performed light-saturated experimental manipulations on surface ocean microbial communities from McMurdo Sound in the Ross Sea to examine the effects of increased iron availability (+2 nM) and warming (+3 and +6 °C) on nutrient uptake, as well as the growth and transcriptional responses of two dominant diatoms, Fragilariopsis and Pseudo-nitzschia. We found that community nutrient uptake and primary productivity were elevated under both warming conditions without iron addition (relative to ambient −0.5 °C). This effect was greater than additive under concurrent iron addition and warming. Pseudo-nitzschia became more abundant under warming without added iron (especially at 6 °C), while Fragilariopsis only became more abundant under warming in the iron-added treatments. We attribute the apparent advantage Pseudo-nitzschia shows under warming to up-regulation of iron-conserving photosynthetic processes, utilization of iron-economic nitrogen assimilation mechanisms, and increased iron uptake and storage. These data identify important molecular and physiological differences between dominant diatom groups and add to the growing body of evidence for Pseudo-nitzschia’s increasingly important role in warming SO ecosystems. This study also suggests that temperature-driven shifts in SO phytoplankton assemblages may increase utilization of the vast pool of excess nutrients in iron-limited SO surface waters and thereby influence global nutrient distribution and carbon cycling.

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Molecular underpinnings and biogeochemical consequences of enhanced diatom growth in a warming Southern Ocean

10.1101/2020.07.01.177865 ◽

2020 ◽

Author(s):

Loay Jabre ◽

Andrew E. Allen ◽

J. Scott P. McCain ◽

John P. McCrow ◽

Nancy Tenenbaum ◽

...

Keyword(s):

Southern Ocean ◽

Ross Sea ◽

Iron Availability ◽

Phytoplankton Blooms ◽

Phytoplankton Assemblages ◽

Carbon Cycles ◽

Cellular Iron ◽

Increased Temperature ◽

The Face ◽

Iron Addition

AbstractThe Southern Ocean (SO) harbours some of the most intense phytoplankton blooms on Earth. Changes in temperature and iron availability are expected to alter the intensity of SO phytoplankton blooms, but little is known about how environmental change will influence community composition and downstream biogeochemical processes. We performed experimental manipulations on surface ocean microbial communities from McMurdo Sound in the Ross Sea, with and without iron addition, at −0.5 °C, 3 °C, and 6 °C. We then examined nutrient uptake patterns as well as the growth and molecular responses of two dominant diatoms, Fragilariopsis and Pseudo-nitzschia, to these conditions. We found that nitrate uptake and primary productivity were elevated at increased temperature in the absence of iron addition, and were even greater at high temperature with added iron. Pseudo-nitzschia became more abundant under increased temperature without added iron, while Fragilariopsis required additional iron to benefit from warming. We attribute the apparent advantage Pseudo-nitzschia shows under warming to upregulation of iron-conserving photosynthetic processes, utilization of iron-economic nitrogen assimilation mechanisms, and increased iron uptake and storage. These data identify important molecular and physiological differences between dominant diatom groups and add to the growing body of evidence for Pseudo-nitzschia’s increasingly important role in warming SO ecosystems. This study also suggests that temperature-driven shifts in SO phytoplankton assemblages may increase utilization of the vast pool of excess nutrients in iron-limited SO surface waters, and thereby influence global nutrient distributions and carbon cycle.Significance StatementPhytoplankton assemblages contribute to the Southern Ocean’s ability to absorb atmospheric CO2, form the base of marine food webs, and shape the global distribution of macronutrients. Anthropogenic climate change is altering the SO environment, yet we do not fully understand how resident phytoplankton will react to this change. By comparing the responses of two prominent SO diatom groups to changes in temperature and iron in a natural community, we find that one group, Pseudo-nitzschia, grows better under warmer low-iron conditions by managing cellular iron demand and efficiently increasing photosynthetic capacity. This ability to grow and draw down nutrients in the face of warming, regardless of iron availability, may have major implications for ocean ecosystems and global nutrient and carbon cycles.

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Factors controlling the competition between <i>Phaeocystis</i> and diatoms in the Southern Ocean

10.5194/bg-2019-488 ◽

2020 ◽

Author(s):

Cara Nissen ◽

Meike Vogt

Keyword(s):

Southern Ocean ◽

High Latitude ◽

Phytoplankton Community ◽

Ecological Model ◽

Ross Sea ◽

Light Sensitivity ◽

Relative Importance ◽

Iron Availability ◽

Poc Export ◽

Biomass Loss

Abstract. The high-latitude Southern Ocean phytoplankton community is shaped by the competition between Phaeocystis and silicifying diatoms, with the relative abundance of these two groups controlling primary and export production, the production of dimethylsulfide, the ratio of silicic acid and nitrate available in the water column, and the structure of the food web. Here, we investigate this competition using a regional physical-biogeochemical-ecological model (ROMS-BEC) configured at eddy-permitting resolution for the Southern Ocean south of 35° S. We extended ROMS-BEC by an explicit parameterization of Phaeocystis colonies, so that the model, together with the previous addition of an explicit coccolithophore type, now includes all biogeochemically relevant Southern Ocean phytoplankton types. We find that Phaeocystis contribute 46 % and 40 % to annual NPP and POC export south of 60° S, respectively, making them an important contributor to high-latitude carbon cycling. In our simulation, the relative importance of Phaeocystis and diatoms is mainly controlled by the temporal variability in temperature and iron availability. The higher light sensitivity of Phaeocystis at low irradiances promotes the succession from Phaeocystis to diatoms in more coastal areas, such as the Ross Sea. Still, differences in the biomass loss rates, such as aggregation or grazing by zooplankton, need to be considered to explain the simulated seasonal biomass evolution.

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The effect of in situ iron addition on the sinking rates and export flux of Southern Ocean diatoms

Deep Sea Research Part II Topical Studies in Oceanography ◽

10.1016/s0967-0645(01)00012-1 ◽

2001 ◽

Vol 48 (11-12) ◽

pp. 2635-2654 ◽

Cited By ~ 71

Author(s):

Anya M Waite ◽

Scott D Nodder

Keyword(s):

Southern Ocean ◽

Export Flux ◽

Iron Addition

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MPAs in the Southern Ocean under CCAMLR

The Korean Journal of International and Comparative Law ◽

10.1163/22134484-12340147 ◽

2021 ◽

Vol 9 (1) ◽

pp. 84-107

Author(s):

Karen N. Scott

Keyword(s):

Southern Ocean ◽

Protected Area ◽

Marine Protected Area ◽

Ross Sea ◽

Coastal Areas ◽

Antarctic Marine ◽

National Jurisdiction

Abstract In 2016, the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) designated the largest marine protected area (MPA) in the Ross Sea. Hailed as both a precedent and a prototype for MPAs in both Antarctica and in areas beyond national jurisdiction more generally, it is nevertheless proving challenging to implement. Moreover, further MPAs have yet to be designated in the region although a number are under negotiation. This article will evaluate the contribution made by CCAMLR to the implementation of SDG 14.5 (the conservation of at least 20 per cent of marine and coastal areas by 2020), its relationship to area-based protection under the 1991 Environmental Protocol, and highlight the challenges of establishing MPAs beyond the jurisdiction of states.

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Modeling the effect of Ross Ice Shelf melting on the Southern Ocean in quasi-equilibrium

The Cryosphere ◽

10.5194/tc-12-3033-2018 ◽

2018 ◽

Vol 12 (9) ◽

pp. 3033-3044 ◽

Cited By ~ 1

Author(s):

Xiying Liu

Keyword(s):

Southern Ocean ◽

Sea Ice ◽

Ross Sea ◽

Global Ocean ◽

Freshwater Flux ◽

Quasi Equilibrium ◽

Ice Shelf ◽

Sea Ice Concentration ◽

Ross Ice Shelf ◽

Ice Concentration

Abstract. To study the influence of basal melting of the Ross Ice Shelf (BMRIS) on the Southern Ocean (ocean southward of 35∘ S) in quasi-equilibrium, numerical experiments with and without the BMRIS effect were performed using a global ocean–sea ice–ice shelf coupled model. In both experiments, the model started from a state of quasi-equilibrium ocean and was integrated for 500 years forced by CORE (Coordinated Ocean-ice Reference Experiment) normal-year atmospheric fields. The simulation results of the last 100 years were analyzed. The melt rate averaged over the entire Ross Ice Shelf is 0.25 m a−1, which is associated with a freshwater flux of 3.15 mSv (1 mSv = 103 m3 s−1). The extra freshwater flux decreases the salinity in the region from 1500 m depth to the sea floor in the southern Pacific and Indian oceans, with a maximum difference of nearly 0.005 PSU in the Pacific Ocean. Conversely, the effect of concurrent heat flux is mainly confined to the middle depth layer (approximately 1500 to 3000 m). The decreased density due to the BMRIS effect, together with the influence of ocean topography, creates local differences in circulation in the Ross Sea and nearby waters. Through advection by the Antarctic Circumpolar Current, the flux difference from BMRIS gives rise to an increase of sea ice thickness and sea ice concentration in the Ross Sea adjacent to the coast and ocean water to the east. Warm advection and accumulation of warm water associated with differences in local circulation decrease sea ice concentration on the margins of sea ice cover adjacent to open water in the Ross Sea in September. The decreased water density weakens the subpolar cell as well as the lower cell in the global residual meridional overturning circulation (MOC). Moreover, we observe accompanying reduced southward meridional heat transport at most latitudes of the Southern Ocean.

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Holodentata gen. nov. (Isopoda: Asellota: Paramunnidae) with a description of two new species: H. caeca and H. triangulata from the Southern Ocean

Zootaxa ◽

10.11646/zootaxa.2096.1.24 ◽

2009 ◽

Vol 2096 (1) ◽

pp. 395-412 ◽

Cited By ~ 2

Author(s):

BRENDA LÍA DOTI ◽

MADHUMITA CHOUDHURY ◽

ANGELIKA BRANDT

Keyword(s):

New Species ◽

Southern Ocean ◽

Dorsal View ◽

Type Species ◽

New Genus ◽

Ross Sea ◽

Weddell Sea ◽

Two New Species

A new genus of Paramunnidae, Holodentata (type species: Paramunna gaussi Vanhöffen, 1914) is erected. The new genus comprises two new species: H. caeca, from the deep Weddell Sea and H. triangulata, from the Ross Sea. The new genus is distinguished by the following characters: article 3 of the antenna short and with strong denticles, mandible palp absent, article 2 of maxilliped palp longest, coxal plates visible in dorsal view in all pereonites, pleotelson broad and laterally denticulated.

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Contribution of changes in opal productivity and nutrient distribution in the coastal upwelling systems to Late Pliocene/Early Pleistocene climate cooling

Climate of the Past ◽

10.5194/cp-8-1435-2012 ◽

2012 ◽

Vol 8 (5) ◽

pp. 1435-1445 ◽

Cited By ~ 17

Author(s):

J. Etourneau ◽

C. Ehlert ◽

M. Frank ◽

P. Martinez ◽

R. Schneider

Keyword(s):

Southern Ocean ◽

Coastal Upwelling ◽

Atmospheric Co2 ◽

Early Pleistocene ◽

Silicon Isotope ◽

Time Interval ◽

Nutrient Distribution ◽

Biogenic Opal ◽

Late Pliocene ◽

Polar Ocean

Abstract. The global Late Pliocene/Early Pleistocene cooling (~3.0–2.0 million years ago – Ma) concurred with extremely high diatom and biogenic opal production in most of the major coastal upwelling regions. This phenomenon was particularly pronounced in the Benguela upwelling system (BUS), off Namibia, where it is known as the Matuyama Diatom Maximum (MDM). Our study focuses on a new diatom silicon isotope (δ30Si) record covering the MDM in the BUS. Unexpectedly, the variations in δ30Si signal follow biogenic opal content, whereby the highest δ30Si values correspond to the highest biogenic opal content. We interpret the higher δ30Si values during the MDM as a result of a stronger degree of silicate utilisation in the surface waters caused by high productivity of mat-forming diatom species. This was most likely promoted by weak upwelling intensity dominating the BUS during the Late Pliocene/Early Pleistocene cooling combined with a large silicate supply derived from a strong Southern Ocean nutrient leakage responding to the expansion of Antarctic ice cover and the resulting stratification of the polar ocean 3.0–2.7 Ma ago. A similar scenario is hypothesized for other major coastal upwelling systems (e.g. off California) during this time interval, suggesting that the efficiency of the biological carbon pump was probably sufficiently enhanced in these regions during the MDM to have significantly increased the transport of atmospheric CO2 to the deep ocean. In addition, the coeval extension of the area of surface water stratification in both the Southern Ocean and the North Pacific, which decreased CO2 release to the atmosphere, led to further enhanced atmospheric CO2 drawn-down and thus contributed significantly to Late Pliocene/Early Pleistocene cooling.

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Biogenic silica concentrations collected from CTD casts during RVIB Nathaniel B. Palmer cruise in the Ross Sea, Southern Ocean from 2017-2018

Biological and Chemical Oceanography Data Management Office ◽

10.1575/1912/bco-dmo.780191.1 ◽

2019 ◽

Author(s):

Giacomo DiTullio ◽

Peter Lee

Keyword(s):

Southern Ocean ◽

Biogenic Silica ◽

Ross Sea

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Carbonate saturation state of surface waters in the Ross Sea and Southern Ocean: controls and implications for the onset of aragonite undersaturation

Biogeosciences Discussions ◽

10.5194/bgd-12-8429-2015 ◽

2015 ◽

Vol 12 (11) ◽

pp. 8429-8465 ◽

Cited By ~ 3

Author(s):

H. B. DeJong ◽

R. B. Dunbar ◽

D. A. Mucciarone ◽

D. A. Koweek

Keyword(s):

Southern Ocean ◽

Surface Waters ◽

Ross Sea ◽

Polar Front ◽

Early Spring ◽

Total Alkalinity ◽

Saturation State ◽

System Data ◽

Algal Photosynthesis ◽

Carbon System

Abstract. Predicting when surface waters of the Ross Sea and Southern Ocean will become undersaturated with respect to biogenic carbonate minerals is challenging in part due to the lack of baseline high resolution carbon system data. Here we present ~ 1700 surface total alkalinity measurements from the Ross Sea and along a transect between the Ross Sea and southern Chile from the austral autumn (February–March 2013). We calculate the saturation state of aragonite (ΩAr) and calcite (ΩCa) using measured total alkalinity and pCO2. In the Ross Sea and south of the Polar Front, variability in carbonate saturation state (Ω) is mainly driven by algal photosynthesis. Freshwater dilution and calcification have minimal influence on Ω variability. We estimate an early spring surface water ΩAr value of ~ 1.2 for the Ross Sea using a total alkalinity–salinity relationship and historical pCO2 measurements. Our results suggest that the Ross Sea is not likely to become undersaturated with respect to aragonite until the year 2070.

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