Non-linear response of summertime marine productivity to increased meltwater discharge around Greenland

Hopwood, Mark J.; Carroll, Dustin; Browning, Thomas J.; Meire, Lorenz; Mortensen, John; Krisch, Stephan; Achterberg, Eric P.

doi:10.1038/s41467-018-05488-8

Cited by 141 publications

(200 citation statements)

References 73 publications

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“…This accords with results from previous studies elsewhere in the North Atlantic (Blain et al ; Moore et al ; Nielsdóttir et al 2009; Ryan‐Keogh et al ). Transitions in limiting nutrients fit within an overall seasonal shift in the bottom‐up resource controls on phytoplankton growth (Ryan‐Keogh et al ): from early season light limitation, transitioning to Fe limitation, and subsequently, N limitation where winter mixed layer nitrate inventories are lower and/or Fe supply is higher (Moore et al ; Achterberg et al ; Ryan‐Keogh et al ; Achterberg et al ; Hopwood et al ; Sedwick et al ; Birchhill et al 2019). In combination with top‐down grazer control, either or both nutrients could therefore sufficiently slow growth rates of larger phytoplankton to terminate the spring bloom (Banse ; Ryan‐Keogh et al ; Behrenfeld and Boss ).…”

Section: Resultsmentioning

confidence: 98%

Nutrient regulation of late spring phytoplankton blooms in the midlatitude North Atlantic

Browning

Al‐Hashem

Hopwood

et al. 2019

Limnology & Oceanography

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The duration and magnitude of the North Atlantic spring bloom impacts both higher trophic levels and oceanic carbon sequestration. Nutrient exhaustion offers a general explanation for bloom termination, but detail on which nutrients and their relative influence on phytoplankton productivity, community structure, and physiology is lacking. Here, we address this using nutrient addition bioassay experiments conducted across the midlatitude North Atlantic in June 2017 (late spring). In four out of six experiments, phytoplankton accumulated over 48–72 h following individual additions of either iron (Fe) or nitrogen (N). In the remaining two experiments, Fe and N were serially limiting, that is, their combined addition sequentially enhanced phytoplankton accumulation. Silicic acid (Si) added in combination with N + Fe led to further chlorophyll a (Chl a) enhancement at two sites. Conversely, addition of zinc, manganese, cobalt, vitamin B12, or phosphate in combination with N + Fe did not. At two sites, the simultaneous supply of all six nutrients, in combination with N + Fe, also led to no further Chl a enhancement, but did result in an additional 30–60% particulate carbon accumulation. This particulate carbon accumulation was not matched by a Redfield equivalent of particulate N, characteristic of high C:N organic exudates that enhance cell aggregation and sinking. Our results suggest that growth rates of larger phytoplankton were primarily limited by Fe and/or N, making the availability of these nutrients the main bottom‐up factors contributing to spring bloom termination. In addition, the simultaneous availability of other nutrients could modify bloom characteristics and carbon export efficiency.

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Section: Resultsmentioning

confidence: 98%

Nutrient regulation of late spring phytoplankton blooms in the midlatitude North Atlantic

Browning

Al‐Hashem

Hopwood

et al. 2019

Limnology & Oceanography

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“…Interactions between the ocean and ice sheet fundamentally impact the biogeochemistry and structure of marine ecosystems in glacial fjords along the coast of Greenland. High rates of summertime primary productivity and phytoplankton biomass, coincident with nutrient enrichment of the upper water column downstream of marine-terminating glaciers, have been attributed to the sustained upwelling of deep, nutrient-rich ocean waters entrained as a result of subglacial discharge (Meire et al, 2017;Overeem et al, 2017;Hopwood et al, 2018;Kanna et al, 2018;Cape et al, 2019). This upwelling of nutrients is also thought to contribute to a lengthening of the growth season within glacial fjords, with secondary summer blooms accounting for an unusually large fraction of annual primary production (Juul-Pedersen et al, 2015).…”

Section: Impact On Ocean Biogeochemistry and Marine Ecosystemsmentioning

confidence: 99%

The Case for a Sustained Greenland Ice Sheet-Ocean Observing System (GrIOOS)

et al. 2019

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Rapid mass loss from the Greenland Ice Sheet (GrIS) is affecting sea level and, through increased freshwater and sediment discharge, ocean circulation, sea-ice, biogeochemistry, and marine ecosystems around Greenland. Key to interpreting ongoing and projecting future ice loss, and its impact on the ocean, is understanding exchanges of heat, freshwater, and nutrients that occur at the GrIS marine margins. Processes governing these exchanges are not well understood because of limited observations from the regions where glaciers terminate into the ocean and the challenge of modeling the spatial and temporal scales involved. Thus, notwithstanding their importance, ice sheet/ocean exchanges are poorly represented or not accounted for in models used for projection studies. Widespread community consensus maintains that concurrent and long-term records of glaciological, oceanic, and atmospheric parameters at the ice sheet/ocean margins are key to addressing this knowledge gap by informing understanding, and constraining and validating models. Through a series of workshops and documents endorsed by the community-at-large, a framework for an international, collaborative, Greenland Ice sheet-Ocean Observing System (GrIOOS), that addresses the needs of society in relation to a changing GrIS, has been proposed. This system would consist of a set of ocean, glacier, and atmosphere essential variables to be collected at a number of diverse sites around Greenland for a minimum of two decades. Internationally agreed upon data protocols and data sharing policies would guarantee uniformity and availability of the information for the broader community. Its

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“…Several sources contribute to the Fe pool in the SO: atmospheric dust deposition (Wagener et al, 2008;Tagliabue et al, 2009;Boyd et al, 2010aBoyd et al, , 2012Hooper et al, 2019;Ito et al, 2019), sediment resuspension and dissolution (Dulaiova et al, 2009;Tagliabue et al, 2009;de Jong et al, 2013;Borrione et al, 2014), hydrothermal activity (Tagliabue et al, 2010), iceberg calving and melting (Smith et al, 2007;Lin et al, 2011;Duprat et al, 2016;Raiswell et al, 2016), ice shelves (Gerringa et al, 2012;Herraiz-Borreguero et al, 2016;St-Laurent et al, 2017), and sea ice (Lannuzel et al, 2007(Lannuzel et al, , 2010(Lannuzel et al, , 2016Lancelot et al, 2009). Modeling studies have highlighted the different levels of significance of these Fe sources to sustain primary productivity in the SO (Lancelot et al, 2009;Tagliabue et al, 2009Tagliabue et al, , 2014aBorrione et al, 2014;Death et al, 2014;Wadley et al, 2014;Wang et al, 2014;Laufkötter et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

Sensitivity of ocean biogeochemistry to the iron supply from the Antarctic Ice Sheet explored with a biogeochemical model

et al. 2019

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Abstract. Iron (Fe) delivery by the Antarctic Ice Sheet (AIS) through ice shelf and iceberg melting enhances primary productivity in the largely iron-limited Southern Ocean (SO). To explore this fertilization capacity, we implement a simple representation of the AIS iron source in the global ocean biogeochemical model NEMO-PISCES. We evaluate the response of Fe, surface chlorophyll, primary production, and carbon (C) export to the magnitude and hypothesized vertical distributions of the AIS Fe fluxes. Surface Fe and chlorophyll concentrations are increased up to 24 % and 12 %, respectively, over the whole SO. The AIS Fe delivery is found to have a relatively modest impact on SO primary production and C export, which are increased by 0.063±0.036 PgC yr−1 and 0.028±0.016, respectively. However, in highly fertilized areas, primary production and C export can be increased by up to 30 % and 42 %, respectively. Icebergs are predicted to have a much larger impact on Fe, surface chlorophyll, and primary productivity than ice shelves in the SO. The response of surface Fe and chlorophyll is maximum in the Atlantic sector, northeast of the tip of the Antarctic Peninsula, and along the East Antarctic coast. The iceberg Fe delivery below the mixed layer may, depending on its assumed vertical distribution, fuel a non-negligible subsurface reservoir of Fe. The AIS Fe supply is effective all year round. The seasonal variations of the iceberg Fe fluxes have regional impacts that are small for annual mean primary productivity and C export at the scale of the SO.

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Non-linear response of summertime marine productivity to increased meltwater discharge around Greenland

Cited by 141 publications

References 73 publications

Nutrient regulation of late spring phytoplankton blooms in the midlatitude North Atlantic

Nutrient regulation of late spring phytoplankton blooms in the midlatitude North Atlantic

The Case for a Sustained Greenland Ice Sheet-Ocean Observing System (GrIOOS)

Sensitivity of ocean biogeochemistry to the iron supply from the Antarctic Ice Sheet explored with a biogeochemical model

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