Major nutrients and dissolved oxygen as indicators of the frontal zones in the Atlantic sector of the Southern Ocean

Abstract

[1] The chemical tracers of the main frontal zones of the Atlantic sector of the Southern Ocean are considered. Before the beginning of the spring bloom, frontal zones are distinguished by lateral gradients of dissolved oxygen, phosphate, nitrate, and silicate. During the spring bloom, the smoothing of nutrient concentrations on both sides of the fronts weakens lateral gradients of chemical properties. The position of surface gradients of nutrients within the Subtropical Frontal Zone (STFZ) does not coincide with the location of temperature and salinity gradients. As a result, fronts in this region have a stepped character. The best chemical indicator of the Northern STFZ front is the dissolved oxygen gradient, which coincides with the temperature and salinity gradients. The southern boundary of the STFZ is distinguished by the gradient of nitrate. The chemical criterion for identifying the Subantarctic Front is the gradient of oxygen, which ranges from 0.5 to 4.0 mmol kg À1 per km; the Polar Front is identified by the gradient of silicate (0.56 to 2.78 mM per km). At the surface, the Weddell-Scotia Confluence (WSC) is distinguished not by the temperature and salinity, but by chemical parameters: The best year-round criterion is the lateral gradient of silicate-to-phosphate atomic ratio, which ranges from 25 to 35. Other markers of the WSC are the gradients of silicate at the surface, oxygen at the upper boundary of the Circumpolar Deep Water, and the depths of its location.

Fronts and surface zonal geostrophic current along 115°E in the southern Indian Ocean

“…The SAF in our study section was found near 46 • S (Fig.2). This location is consistent with previous studies (Hofmann, 1985;Belkin and Gordon, 1996;Dafner, 2003;Yuan et al, 2004;Aoki et al, 2007). The path of the SAF shows a general southward displacement in the Southern Indian Ocean (Orsi et al, 1995;Belkin and Gordon, 1996).…”

“…Here we use the phenomenological criteria to identify oceanic fronts in the Southern Ocean, i.e., adopting the quasi-permanent nature of frontal properties (Dafner, 2003).…”

On the drivers of phytoplankton blooms in the Antarctic marginal ice zone: A modeling approach

“…Holm‐Hansen et al ., ; Sokolov and Rintoul , ]. In open water, the timing and intensity of the spring bloom varies greatly, probably on account of water mass interactions [ Dafner et al ., ].…”

“…The seasonal ice zone (SIZ) extends hundreds of kilometers from the Antarctic coast [ Sakshaug et al ., ] with sea ice typically being less than 1 m thick [ Pfaffling et al ., ] and growing from April and melting from October. The offshore water masses are characterized by latitudinal gradients in nutrients during the winter, which reflect the circumpolar frontal structure [ Dafner et al ., ]. The major fronts are found at 40°S (sub‐tropical front), 45°S (sub‐Antarctic front), 50°S (Antarctic polar front), and ca.…”

Air‐sea CO2 flux variability in frontal regions of the Southern Ocean from CARbon Interface OCean Atmosphere drifters

“…A primary difficulty when working with autonomous surface drifters is how to characterize their location with respect to hydrography. Multiple criteria have been defined to identify hydrological fronts, based either on vertical properties (Orsi et al 1995;Belkin and Gordon 1996) or on surface properties (Dafner et al 2003). In this paper, we test several methods for identifying the subantarctic front (SAF) from satellite data based either on sea surface temperature (SST) or on sea-level anomaly gradients.…”