Physical and Biogeochemical Regionalization of the Southern Ocean and the CCAMLR Zone 48.1

Giovanni Testa,Andrea Piñones,Leonardo R Castro

doi:10.3389/fmars.2021.592378

Abstract

The Southern Ocean plays a major role in the Earth’s climate, provides fisheries products and help the maintenance of biodiversity. The degree of correspondence between physical and biogeochemical spatial variability and regionalization were investigated by calculating the main physical factors that statistically explained the biogeochemical variability within the Southern Ocean and the 48.1 zone of the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR). The mean value of physical and biogeochemical variables was estimated during austral summer within a grid of 1° × 1° south of 50°S. The regionalization was developed using both non-hierarchical and hierarchical clustering method, whereas BIO-ENV package and distance-based redundancy analysis (db-RDA) were applied in order to calculate which physical factors primarily explained the biogeochemical spatial variability. A total of 12 physical and 18 biogeochemical significant clusters were identified for the Southern Ocean (alpha: 0.05). The combination of bathymetry and sea ice coverage majorly explained biogeochemical variability (Spearman rank correlation coefficient: 0.68) and db-RDA indicated that physical variables expressed the 60.1% of biogeochemical variance. On the other hand, 14 physical and 16 biogeochemical significant clusters were identified for 48.1 CCAMLR zone. Bathymetry was the main factor explaining biogeochemical variability (Spearman coefficient: 0.81) and db-RDA analysis resulted in 77.1% of biogeochemical variance. The correspondence between physical and biogeochemical regions was higher for CCAMLR 48.1 zone with respect to the whole Southern Ocean. Our results provide useful information for both Southern Ocean and CCAMLR 48.1 zone ecosystem management and modeling parametrization.

Highlights

The Southern Ocean plays a major role in the Earth’s climate since the opening of the Drake Passage approximately 41 Ma ago (Scher and Martin, 2006)
The export of Particulate Organic Carbon (POC) south of 50◦S is 1000 Tg C yr−1 corresponding to 10% of the global POC export, with a significant contribution of dissolved organic carbon in the top 500 m of the water column (Schlitzer, 2002)
The limits of the CCAMLR 48.1 zone (50–70◦W, 60–70◦S with the exclusion of the of the southern part of the Weddell Sea) are very similar to those that define the Western Antarctic Peninsula and Scotia Arc zone identified by the Southern Ocean Observing System1

Summary

INTRODUCTION

The Southern Ocean plays a major role in the Earth’s climate since the opening of the Drake Passage approximately 41 Ma ago (Scher and Martin, 2006). The 48.1 zone of the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) is a key region for monitoring the Antarctic ecosystem This area is experimenting strong interannual variability and trends in sea ice coverage and water column temperature (Schmidtko et al, 2014; Jones et al, 2016) that turn this zone in one of the most climate sensitive region of the planet and most variable (Hendry et al, 2018). Recent studies (Murphy et al, 2016; Comiso et al, 2017) suggested that the interannual oceanographic variability is partly linked with atmospheric patterns, such as El Niño-Southern Oscillation and the Southern Annular Mode This region is subject to strong anthropic influence via krill fisheries (Boyd, 2009; Ainley and Pauly, 2014; McBride et al, 2014) and local contamination by increasing tourist’s presence (Bargagli, 2008; Waller et al, 2017). The work will deliver useful information to the scientific community in order to identify highly productive areas and to understand and predict future changes in the context of the current climate crisis

MATERIALS AND METHODS

RESULTS

DISCUSSION

CONCLUSION

DATA AVAILABILITY STATEMENT