Dominant role of eddies and filaments in the offshore transport of carbon and nutrients in the <scp>C</scp>alifornia <scp>C</scp>urrent <scp>S</scp>ystem

Nagai, Takeyoshi; Gruber, Nicolas; Frenzel, Hartmut; Lachkar, Zouhair; McWilliams, James C.; Plattner, Gian‐Kasper

doi:10.1002/2015jc010889

Cited by 140 publications

(211 citation statements)

References 80 publications

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“…The quantification of this export is notoriously difficult to achieve through in situ studies owing to the intermittency of the transport and the importance of eddies, filaments, and other turbulent structures (e.g., Peliz et al, 2004;Nagai et al, 2015), providing models an opportunity to fill the gap. These models need to have relatively high resolution in order to resolve these mesoscale dynamics, forcing most studies to employ regional models instead of global ones.…”

Section: Introductionmentioning

confidence: 99%

On the long-range offshore transport of organic carbon from the Canary Upwelling System to the open North Atlantic

Lovecchio¹,

Gruber²,

Münnich³

et al. 2017

Biogeosciences

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106

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Abstract. A compilation of measurements of net community production (NCP) in the upper waters of the eastern subtropical North Atlantic had suggested net heterotrophic conditions, purportedly supported by the lateral export of organic carbon from the adjacent, highly productive Canary Upwelling System (CanUS). Here, we quantify and assess this lateral export using the Regional Ocean Modeling System (ROMS) coupled to a nutrient, phytoplankton, zooplankton, and detritus (NPZD) ecosystem model. We employ a new Atlantic telescopic grid with a strong refinement towards the northwestern African shelf to combine an eddy-resolving resolution in the CanUS with a full Atlantic basin perspective. Our climatologically forced simulation reveals an intense offshore flux of organic carbon that transports about 19 Tg C yr −1 away from the nearshore 100 km over the whole CanUS, amounting to more than a third of the NCP in this region. The offshore transport extends beyond 1500 km into the subtropical North Atlantic, adding organic carbon along the way to the upper 100 m at rates of between 8 and 34 % of the alongshore average NCP as a function of offshore distance. Although the divergence of this lateral export of organic carbon enhances local respiration, the upper 100 m layer in our model remains net autotrophic in the entire eastern subtropical North Atlantic. However, the vertical export of this organic carbon and its subsequent remineralization at depth makes the vertically integrated NCP strongly negative throughout this region, with the exception of a narrow band along the northwestern African shelf. The magnitude and efficiency of the lateral export varies substantially between the different subregions. In particular, the central coast near Cape Blanc is particularly efficient in collecting organic carbon on the shelf and subsequently transporting it offshore. In this central subregion, the offshore transport adds as much organic carbon as nearly 60 % of the local NCP to the upper 100 m, giving rise to a sharp peak of offshore respiration that extends to the middle of the gyre. Our modeled offshore transport of organic carbon is likely a lower-bound estimate due to our lack of full consideration of the contribution of dissolved organic carbon and that of particulate organic carbon stemming from the resuspension of sediments. But even in the absence of these contributions, our results emphasize the fundamental role of the lateral redistribution of the organic carbon for the maintenance of the heterotrophic activity in the open sea.

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Section: Introductionmentioning

confidence: 99%

On the long-range offshore transport of organic carbon from the Canary Upwelling System to the open North Atlantic

Lovecchio¹,

Gruber²,

Münnich³

et al. 2017

Biogeosciences

Self Cite

106

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“…Monthly, multiyear time-series of productivity, based on incubations measuring the uptake of 14 C-labeled dissolved inorganic carbon (DIC) and 15 NO − 3 have been reported previously (Pennington and Chavez, 2000;Wilkerson et al, 2000), and numerous process-oriented biological studies have been conducted (Pilskaln et al, 1996;Kudela and Dugdale, 2000;Ward, 2005;Ryan et al, 2009;Johnson, 2010;Smith et al, 2014aSmith et al, , 2016 , but can be challenging to apply in systems where recently-upwelled water is observed at the surface; this low O 2 water may bias estimates low if not accurately accounted for (Munro et al, 2013;Teeter, 2014;Haskell et al, 2016b). Furthermore, inferring carbon export below the mixed layer from techniques within the mixed layer is complicated by the fact that lateral transport of surface waters and oceanic fronts may cause a spatial and/or temporal decoupling between carbon fixation and export (Olivieri and Chavez, 2000;Estapa et al, 2015;Nagai et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

Insight into chemical, biological, and physical processes in coastal waters from dissolved oxygen and inert gas tracers

Manning¹

2017

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In this thesis, I use coastal measurements of dissolved O 2 and inert gases to provide insight into the chemical, biological, and physical processes that impact the oceanic cycles of carbon and dissolved gases. Dissolved O 2 concentration and triple isotopic composition trace net and gross biological productivity. The saturation states of inert gases trace physical processes, such as air-water gas exchange, temperature change, and mixing, that affect all gases.First, I developed a field-deployable system that measures Ne, Ar, Kr, and Xe gas ratios in water. It has precision and accuracy of 1 % or better, enables near-continuous measurements, and has much lower cost compared to existing laboratory-based methods. The system will increase the scientific community's access to use dissolved noble gases as environmental tracers.Second, I measured O 2 and five noble gases during a cruise in Monterey Bay, California. I developed a vertical model and found that accurately parameterizing bubble-mediated gas exchange was necessary to accurately simulate the He and Ne measurements. I present the first comparison of multiple gas tracer, incubation, and sediment trap-based productivity estimates in the coastal ocean. Net community production estimated from 15 NO -3 uptake and O 2 /Ar gave equivalent results at steady state. Underway O 2 /Ar measurements revealed submesoscale variability that was not apparent from daily incubations.Third, I quantified productivity by O 2 mass balance and air-water gas exchange by dual tracer ( 3 He/SF 6 ) release during ice melt in the Bras d'Or Lakes, a Canadian estuary. The gas transfer velocity at >90 % ice cover was 6 % of the rate for nearly ice-free conditions. Rates of volumetric gross primary production were similar when the estuary was completely ice-covered and ice-free, and the ecosystem was on average net autotrophic during ice melt and net heterotrophic following ice melt. I present a method for incorporating the isotopic composition of H 2 O into the O 2 isotope-based productivity calculations, which increases the estimated gross primary production in this study by 46-97 %.In summary, I describe a new noble gas analysis system and apply O 2 and inert gas observations in new ways to study chemical, biological, and physical processes in coastal waters.

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“…In particular, since the Peruvian region is the location of relatively intense eddy activity (Chaigneau et al, 2009), the question of whether or not eddy activity is involved in the seasonal variability of the OMZ arises and calls for assessing its contribution to the DO flux. There is growing evidence that the mesoscale activity plays a key role in the biogeochemical cycles and the OMZ structure in eastern boundary upwelling systems (Duteil and Oschlies, 2011;Nagai et al, 2015). Most studies addressing the role of mesoscale processes in the OMZs have focused on the ventilation from the coastal domain, where the primary production bloom provides nutrients and DO anomalies that are in turn transported offshore Czeschel et al, 2015;Thomsen et al, 2016).…”

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confidence: 99%

Seasonal variability of the oxygen minimum zone off Peru in a high-resolution regional coupled model

et al. 2016

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Abstract. In addition to being one of the most productive upwelling systems, the oceanic region off Peru is embedded in one of the most extensive oxygen minimum zones (OMZs) of the world ocean. The dynamics of the OMZ off Peru remain uncertain, partly due to the scarcity of data and to the ubiquitous role of mesoscale activity on the circulation and biogeochemistry. Here we use a high-resolution coupled physical/biogeochemical model simulation to investigate the seasonal variability of the OMZ off Peru. The focus is on characterizing the seasonal cycle in dissolved O 2 (DO) eddy flux at the OMZ boundaries, including the coastal domain, viewed here as the eastern boundary of the OMZ, considering that the mean DO eddy flux in these zones has a significant contribution to the total DO flux. The results indicate that the seasonal variations of the OMZ can be interpreted as resulting from the seasonal modulation of the mesoscale activity. Along the coast, despite the increased seasonal low DO water upwelling, the DO peaks homogeneously over the water column and within the Peru Undercurrent (PUC) in austral winter, which results from mixing associated with the increase in both the intraseasonal wind variability and baroclinic instability of the PUC. The coastal ocean acts therefore as a source of DO in austral winter for the OMZ core, through eddy-induced offshore transport that is also shown to peak in austral winter. In the open ocean, the OMZ can be divided vertically into two zones: an upper zone above 400 m, where the mean DO eddy flux is larger on average than the mean seasonal DO flux and varies seasonally, and a lower part, where the mean seasonal DO flux exhibits verticalzonal propagating features that share similar characteristics than those of the energy flux associated with the annual extratropical Rossby waves. At the OMZ meridional boundaries where the mean DO eddy flux is large, the DO eddy flux has also a marked seasonal cycle that peaks in austral winter (spring) at the northern (southern) boundary. In the model, the amplitude of the seasonal cycle is 70 % larger at the southern boundary than at the northern boundary. Our results suggest the existence of distinct seasonal regimes for the ventilation of the OMZ by eddies at its boundaries. Implications for understanding the OMZ variability at longer timescales are discussed.

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Dominant role of eddies and filaments in the offshore transport of carbon and nutrients in the California Current System

Cited by 140 publications

References 80 publications

On the long-range offshore transport of organic carbon from the Canary Upwelling System to the open North Atlantic

On the long-range offshore transport of organic carbon from the Canary Upwelling System to the open North Atlantic

Insight into chemical, biological, and physical processes in coastal waters from dissolved oxygen and inert gas tracers

Seasonal variability of the oxygen minimum zone off Peru in a high-resolution regional coupled model

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