On the Role of the Gulf Stream in the Changing Atlantic Nutrient Circulation During the 21st Century

Whitt, Daniel B.

doi:10.1002/9781119428428.ch4

Cited by 19 publications

(32 citation statements)

References 143 publications

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“…A10). However, similarly to what has been shown for the North Atlantic in coarse-resolution ESM projections (Whitt, 2019;Whitt and Jansen, 2020;Tagklis et al, 2020), the decrease in nutrient supply is also controlled by the sub-surface nutrient reservoir and the fluxes fueling it. Nitrate concentrations in the top 400 m strongly decrease under our global warming scenario (Fig.…”

Section: Decline In Nutrient Supply Pathwayssupporting

confidence: 60%

“…This lateral nutrient transport is known as the nutrient stream (Williams et al, 2006;Palter and Lozier, 2008;Williams et al, 2011), a strong advective nutrient flux carried in sub-surface waters and associated with western boundary currents (WBCs) and Meridional Overturning Circulation (MOC). Recent results based on ESM projections have suggested that the weakening of the MOC under global warming would reduce the nutrient stream and act in concert with the reduced vertical mixing to induce a decline in NPP (Whitt, 2019;Whitt and Jansen, 2020;Tagklis et al, 2020). An explicit resolution of eddies in ocean models is known to change the position of WBCs (Chassignet and Marshall, 2008;Lévy et al, 2010;Chassignet and Xu, 2017), change the strength of the MOC (Hirschi et al, 2020;Roberts et al, 2020), and increase both stratification (Chanut et al, 2008;Lévy et al, 2010;Karleskind et al, 2011) and the advective supply of nutrients (Lévy et al, 2012a;Uchiyama et al, 2017;Uchida et al, 2020).…”

Section: Introductionmentioning

confidence: 99%

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Oceanic primary production decline halved in eddy-resolving simulations of global warming

Couespel

Lévy

Bopp³

2021

Biogeosciences

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Abstract. The decline in ocean primary production is one of the most alarming consequences of anthropogenic climate change. This decline could indeed lead to a decrease in marine biomass and fish catch, as highlighted by recent policy-relevant reports. Because of computational constraints, current Earth system models used to project ocean primary production under global warming scenarios have to parameterize flows occurring below the resolution of their computational grid (typically 1∘). To overcome these computational constraints, we use an ocean biogeochemical model in an idealized configuration representing a mid-latitude double-gyre circulation and perform global warming simulations under an increasing horizontal resolution (from 1 to 1/27∘) and under a large range of parameter values for the eddy parameterization employed in the coarse-resolution configuration. In line with projections from Earth system models, all our simulations project a marked decline in net primary production in response to the global warming forcing. Whereas this decline is only weakly sensitive to the eddy parameters in the eddy-parameterized coarse 1∘ resolution simulations, the simulated decline in primary production in the subpolar gyre is halved at the finest eddy-resolving resolution (−12 % at 1/27∘ vs. −26 % at 1∘) at the end of the 70-year-long global warming simulations. This difference stems from the high sensitivity of the sub-surface nutrient transport to model resolution. Although being only one piece of a much broader and more complicated response of the ocean to climate change, our results call for improved representation of the role of eddies in nutrient transport below the seasonal mixed layer to better constrain the future evolution of marine biomass and fish catch potential.

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Section: Decline In Nutrient Supply Pathwayssupporting

confidence: 60%

Section: Introductionmentioning

confidence: 99%

Oceanic primary production decline halved in eddy-resolving simulations of global warming

Couespel

Lévy

Bopp³

2021

Biogeosciences

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“…CMIP5 models project that O 2 inventory is likely to decline, but patchy regions of O 2 increase may also occur, driven by declines in AOU transport in the nutrient stream (Tagklis et al, 2017). Analyzing the historical response to anthropogenic forcing of the subpolar air-sea C ant sink and nutrient stream, as well as the future response (e.g., Whitt, 2019) can improve our understanding of the mechanisms driving subpolar C ant uptake. Earth-system models and observations, utilized in complementary fashion, provide a potent framework for the study of regional air-sea C ant uptake in the present and future.…”

Section: Resultsmentioning

confidence: 99%

“…In the future, circulation and biogeochemistry in the subpolar North Atlantic are projected to undergo significant changes (Goris et al, 2018; Halloran et al, 2015; Tagklis et al, 2017; Whitt, 2019). C con uptake is projected to decline mid‐century after an initial period of growth (Halloran et al, 2015).…”

Section: Resultsmentioning

confidence: 99%

“…This interpretation is supported by model experiments (Williams et al, 2006) where idealized tracer released in dense waters of the subtropical North Atlantic outcrops in the subpolar gyre, while tracer released in lighter subtropical surface waters tends to recirculate in the subtropical gyre. Lateral supply of nutrients in the nutrient stream is much greater than supply by Ekman suction within the subpolar gyre (Whitt, 2019; Williams et al, 2006). Thus, studies of both simulated tracer release and observed drifter trajectories indicate that the surface of the subpolar gyre is irrigated from the south with nutrients originating in mode and intermediate waters.…”

Section: Introductionmentioning

confidence: 99%

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Advective Controls on the North Atlantic Anthropogenic Carbon Sink

Ridge

McKinley

2020

Global Biogeochemical Cycles

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Though it is clear that the North Atlantic is the site of the highest storage of anthropogenic carbon (C ant) per area, it is uncertain whether the air-sea C ant fluxes contributing to North Atlantic C ant storage occur in the subpolar gyre or upstream in the subtropical gyre. Using data and models, we show that air-sea C ant uptake capacity is advected into the subpolar gyre along the same subsurface pathway as nutrients. This pathway is known as the nutrient stream. On the A22 section between Woods Hole and Bermuda, nutrient stream waters are the oldest in the upper 2,000 m and contain low C ant. These northward moving waters are sufficiently depleted in C ant such that they could sustain a subpolar air-sea C ant flux of −0.19 Pg C ant year −1. The ocean hindcast model used here indicates that despite some subtropical re-circulation, uptake capacity is transported into the subpolar gyre where it sustains subpolar air-sea C ant uptake. With this model, we show that high-and low-end estimates of subpolar air-sea C ant flux are reconciled by accounting for a factor of two difference in their respective study areas. If half of the observed air-sea C ant uptake capacity transport at A22 is ventilated in the subpolar region, it can fully support high-end estimates of the subpolar air-sea C ant sink (−0.09 ± 0.01 Pg C ant year −1). Plain Language Summary The ocean has absorbed approximately 40% of the CO 2 from fossil fuel burning and cement production, lowering atmospheric CO 2 and limiting climate change. Ocean storage of this additional carbon from human activities (anthropogenic carbon, C ant) is most intense in the North Atlantic. In the subpolar North Atlantic, C ant is injected into the deep ocean and thus sequestered from the atmosphere for thousands of years. It is currently uncertain whether any of this sequestered C ant was absorbed from the atmosphere in the subpolar North Atlantic. Here we present evidence that the upper limb of the ocean's overturning circulation supplies the subpolar North Atlantic with the capacity to absorb C ant from the atmosphere. Subpolar uptake capacity travels along the same subsurface pathways as the nutrients that support subpolar phytoplankton growth. Waters following this pathway likely started their northward journey decades ago, in the Southern Ocean and thus have not been in contact with the high atmospheric carbon concentrations that exist today. When these waters are exposed to the atmosphere in the subpolar North Atlantic, they can absorb a large amount of C ant. We show that this is the mechanism by which the subpolar North Atlantic absorbs a substantial amount of C ant .

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Environmental modulations of nutrient conditions in the Labrador Sea reconstructed from nitrogen isotopes in a six-hundred-year-old crustose coralline alga

Doherty¹,

Williams²,

Kline³

et al. 2020

Preprint

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The climatological impacts on biogeochemical processes in the polar North Atlantic remain poorly understood, as there exist both biological and physical mechanisms that drive nutrient availability in the region. Here, we present nitrogen isotope measurements (δ 15 N) from a sixhundred-year-old coralline alga to elucidate historic and modern trends in Labrador Sea nitrate utilization, defined as the degree of biological nitrate assimilation relative to supply. Prior to the Little Ice Age (LIA), periods during which utilization became complete corresponded to neutral modes of the Atlantic Multidecadal Oscillation (AMO), which we argue promoted the oceanographic conditions favorable for simultaneous phytoplankton growth and reduced nitrate input. More recently, nitrate utilization became complete during periods characterized by reduced deep-water convection in the Labrador Sea, suggesting a reduced inflow of equatoriallysourced nitrate driven by a weakening of the Labrador Current. Such nutrient rerouting may have implications for socioeconomically-important fisheries and carbon sequestration throughout the region.

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On the Role of the Gulf Stream in the Changing Atlantic Nutrient Circulation During the 21st Century

Cited by 19 publications

References 143 publications

Oceanic primary production decline halved in eddy-resolving simulations of global warming

Oceanic primary production decline halved in eddy-resolving simulations of global warming

Advective Controls on the North Atlantic Anthropogenic Carbon Sink

Environmental modulations of nutrient conditions in the Labrador Sea reconstructed from nitrogen isotopes in a six-hundred-year-old crustose coralline alga

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