An advective mechanism for deep chlorophyll maxima formation in southern Drake Passage

Abstract

We observe surface and subsurface fluorescence‐derived chlorophyll maxima in southern Drake Passage during austral summer. Backscatter measurements indicate that the deep chlorophyll maxima (DCMs) are also deep biomass maxima, and euphotic depth estimates show that they lie below the euphotic layer. Subsurface, offshore and near‐surface, onshore features lie along the same isopycnal, suggesting advective generation of DCMs. Temperature measurements indicate a warming of surface waters throughout austral summer, capping the winter water (WW) layer and increasing off‐shelf stratification in this isopycnal layer. The outcrop position of the WW isopycnal layer shifts onshore, into a surface phytoplankton bloom. A lateral potential vorticity (PV) gradient develops, such that a down‐gradient PV flux is consistent with offshore, along‐isopycnal tracer transport. Model results are consistent with this mechanism. Subduction of chlorophyll and biomass along isopycnals represents a biological term not observed by surface satellite measurements which may contribute significantly to the strength of the biological pump in this region.

Distribution of Upper Circumpolar Deep Water on the warming continental shelf of the West Antarctic Peninsula

“…Ocean gliders have significantly improved the spatial resolution of hydrographic measurements along the Antarctic Peninsula, allowing us to resolve features smaller than the spacing of a typical ship‐based survey [ Heywood et al ., ; Erickson et al ., ]. The increased sampling resolution of the gliders increases the likelihood of encountering the small‐scale features containing UCDW.…”

The Seasonality of Physically Driven Export at Submesoscales in the Northeast Atlantic Ocean

“…The effect of these small‐scale vertical motions in bringing nutrients from depth into the euphotic layer and stimulating production is seen in high‐resolution models (Brannigan, ; Lévy et al, ; Mahadevan & Archer, ). Observations also suggest that these vertical motions can subduct water high in chlorophyll below the mixed and euphotic layers (Erickson et al, ; Hood et al, ; Washburn et al, ). The combined effects of submesoscale motions may dominate export in much of the highly productive ocean (Omand et al, ).…”

“…Submesoscale dynamics are particularly active in regimes with large lateral shear, such as boundary currents (Molemaker et al, ; Rocha, Gille, et al, ; Rocha, Chereskin, et al, ; Thomas et al, , ) or the Antarctic Circumpolar Current (Erickson et al, ). However, a growing body of evidence shows that vigorous submesoscale activity is present even in the relatively quiescent open ocean (Brannigan et al, ; Su et al, ; Thompson et al, ).…”

Spatial Variations of Subsurface Chlorophyll Maxima During Thermal Stratification in a Large, Deep Subtropical Reservoir

“…In oceans, deep lakes, and reservoirs, the vertical distribution of chlorophyll (Chl) is uneven, and a subsurface (or deep) chlorophyll maximum is common. The depth of maximum Chl varies from the near-surface to the euphotic depth (Z eu ) during thermal stratification, and peak values and vertical positions can vary with trophic status (Erickson et al, 2016;Leach et al, 2018;Mellard et al, 2011). The subsurface chlorophyll maxima (SCM) are composed of various phytoplankton species, including buoyancy-regulating cyanobacteria (Walsby & Schanz, 2002), flagellates (Clegg et al, 2007;Pannard et al, 2015), and other species (Latasa et al, 2017;Sommer et al, 2012).…”

“…The availability of sensors that record in situ has allowed automated measurements of several water constituents, including temperature and chlorophyll fluorescence (Meinson et al, 2016;Obrador et al, 2014). Chlorophyll fluorescence (ChlF) is a widely used proxy for Chl (Erickson et al, 2016), and ChlF measurements compare favorably with Chl concentrations measured using laboratory methods. Thus, the SCM structure can be determined by ChlF profiles (Leach et al, 2018).…”