Mesoscale Eddies Regulate Seasonal Iron Supply and Carbon Drawdown in the Drake Passage

Abstract

The Southern Ocean plays a critical role in the global carbon cycle. The dominating current in the region, the Antarctic Circumpolar Current (ACC), circumnavigates the globe and connects all of the major ocean basins. Its overturning circulation brings up the deepwater and subducts thermocline and intermediate waters that are major conduits for the oceanic uptake of heat and anthropogenic carbon (Armour et al., 2016; Ben Bronselaer & Zanna, 2020;Toggweiler & Russell, 2008), contributing over 40% of the ocean carbon uptake (Khatiwala et al., 2009). Despite its importance, there are large uncertainties surrounding components controlling the regional carbon flux. While the state-of-the-art Earth System Models (ESMs) generally reproduce the annual mean carbon flux in the region, its seasonal cycle is often poorly correlated with observations (Jiang et al., 2014;Mongwe et al., 2016).The ACC is filled with mesoscale (approx. 10-100 km) features with meandering jets and vortices (eddies) that play central roles to maintain the stratification and the overturning circulation with global implications (Gnanadesikan, 1999;Johnson & Bryden, 1989;Marshall & Radko, 2003;Marshall & Speer, 2012). This rich mesoscale eddy field is critical for the transport of carbon and nutrients in the region, but the current generation of ESMs cannot resolve these features due to their coarse resolution and the challenge of parameterizing eddies realistically.To study the influence of mesoscale eddies on the carbon cycle in this region, we perform and compare three computational simulations for a sensitivity study using a regional physical and biological model with a 10km horizontal resolution. This modeling study is focused on the Drake Passage region, which is the only section of the ACC bounded by land topography to the north and south and relatively well sampled by ship-based

Mesoscale eddies enhance the air-sea CO2 sink in the South Atlantic Ocean

“…showed that mesoscale resolving models may have a modest effect on the global balance of carbon export (<2%), but regionally the effect can be large (±50%). Jersild et al (2021) highlighted that an Earth System Model (ESM) that explicitly resolved mesoscale eddies was able to produce the observed seasonal biological productivity and pCO2 (sw) cycles in the Southern Ocean, but when the eddies were not included, the seasonal cycle was not well reproduced. The results from our study have significant implications on the air-sea CO2 flux in current global ESMs, in which eddies are not explicitly resolved (Hewitt et al, 2017(Hewitt et al, , 2020.…”

Seamless Integration of the Coastal Ocean in Global Marine Carbon Cycle Modeling

“…Yet, we are optimistic that a suitably chosen eddy parameterization will lead to additional improvements of our results, in particular for the general circulation and tracer distribution in the open ocean. The incorporation of subgridscale eddy activity was shown to impact temperature, salinity and sea ice formation in high latitudes (e.g., Knutti et al., 1999; Pradal & Gnanadesikan, 2014) as well as nutrient replenishment in the upper thermocline of oligotrophic subtropical waters (Doddridge & Marshall, 2018; Oschlies, 2008) and seasonal carbon drawdown in the eddy‐rich Southern Ocean (Jersild et al., 2021). The sediment resuspension scheme of ICON‐Coast accounts for the bottom layer thickness in the calculation of the sediment drag coefficient, thus accounting for the vertical grid resolution (Mathis et al., 2019).…”

Seamless integration of the coastal ocean in global marine carbon cycle modeling

“…Yet, we are optimistic that a suitably chosen eddy parameterization will lead to additional improvements of our results, in particular for the general circulation and tracer distribution in the open ocean. The incorporation of subgridscale eddy activity was shown to impact temperature, salinity and sea ice formation in high latitudes (e.g., Knutti et al, 1999;Pradal & Gnanadesikan, 2014) as well as nutrient replenishment in the upper thermocline of oligotrophic subtropical waters (Doddridge & Marshall, 2018;Oschlies, 2008) and seasonal carbon drawdown in the eddy-rich Southern Ocean (Jersild et al, 2021). The sediment resuspension scheme of ICON-Coast accounts for the bottom layer thickness in the calculation of the sediment drag coefficient, thus accounting for the vertical grid resolution (Mathis et al, 2019).…”