Ocean Convection

Abstract

Ocean convection is a key mechanism that regulates heat uptake, water-mass transformation, CO2 exchange, and nutrient transport with crucial implications for ocean dynamics and climate change. Both cooling to the atmosphere and salinification, from evaporation or sea-ice formation, cause surface waters to become dense and down-well as turbulent convective plumes. The upper mixed layer in the ocean is significantly deepened and sustained by convection. In the tropics and subtropics, night-time cooling is a main driver of mixed layer convection, while in the mid- and high-latitude regions, winter cooling is key to mixed layer convection. Additionally, at higher latitudes, and particularly in the sub-polar North Atlantic Ocean, the extensive surface heat loss during winter drives open-ocean convection that can reach thousands of meters in depth. On the Antarctic continental shelf, polynya convection regulates the formation of dense bottom slope currents. These strong convection events help to drive the immense water-mass transport of the globally-spanning meridional overturning circulation (MOC). However, convection is often highly localised in time and space, making it extremely difficult to accurately measure in field observations. Ocean models such as global circulation models (GCMs) are unable to resolve convection and turbulence and, instead, rely on simple convective parameterizations that result in a poor representation of convective processes and their impact on ocean circulation, air–sea exchange, and ocean biology. In the past few decades there has been markedly more observations, advancements in high-resolution numerical simulations, continued innovation in laboratory experiments and improvement of theory for ocean convection. The impacts of anthropogenic climate change on ocean convection are beginning to be observed, but key questions remain regarding future climate scenarios. Here, we review the current knowledge and future direction of ocean convection arising from sea–surface interactions, with a focus on mixed layer, open-ocean, and polynya convection.

Bioluminescence of the tropical Indian Ocean: a multiple‐scale variation

“…The latitudinal pattern implied the weakening of BP from the northern Arabian Sea towards the equatorial region (Figure 2). Presumably, the decline of BP, rests on (1) latitudinally fading convective mixing, which makes the northern Arabian Sea highly productive, [ 28 ] (2) latitudinally fading wind stress that modulate the mixed layer depth, and (3) a global pattern of biomass and biodiversity changes across latitudes. [ 29 ] In particular, the zooplankton biomass and species diversity of the northern Indian Ocean are negatively correlated.…”

“…For instance, a field survey in the equatorial Indian Ocean in 1980, during the summer monsoon and fall intermonsoon, resulted in a significant correlation (r = 0.6-0.8, P > 0.05) of BP and the plankton biomass in the upper 100 m layer that was sampled by nets equipped with 0.13 and 0.08 mm mesh sizes. [28] Moreover, day and nighttime vertical profiles of the BP we obtained along the 68 o E transect (Figure 1c) were markedly different by their vertical fine structure and T A B L E 3 Biophysical characteristics of night stations carried out during the 42nd cruise of R/V Academician Boris Petrov (Figure 1c) BP values (Figure 5). Bathyphotometric casts along the transect were not affected by the eddy we discussed (Figure 3a).…”

“…S: Salinity. The number assigned to a parameter abbreviation stands for the oceanographic station number(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32)…”

Buoyancy forcing and the subpolar Atlantic meridional overturning circulation

“…Convection is an intermittent process in both space and time and involves the interaction of processes at a variety of scales (see comprehensive reviews by [ 75 , 79 ]). The convective process can be thought of as occurring in three phases: (1) preconditioning, (2) deep convection and (3) lateral exchanges, although the last two phases often occur concurrently [ 75 , 80 ].…”

A generic framework for evaluating the oceanic mixed layer depth dynamics

“…Vertical mixing is usually driven by winds, surface cooling, brine rejection, Langmuir turbulence, and wave breaking (Marshall & Schott, 1999;Q. Li et al, 2019;Vreugdenhil & Gayen, 2021). In contrast, restratification processes are driven by solar heating, freshwater flux, or lateral processes such as mixed layer instabilities (see for example Boccaletti et al, 2007;Fox-Kemper et al, 2007).…”