6,000‐Year Reconstruction of Modified Circumpolar Deep Water Intrusion and Its Effects on Sea Ice and Penguin in the Ross Sea

Abstract

The Ross Sea has the world's largest marine protected area. Modified Circumpolar Deep Water (MCDW) has significant effects on physical and biological processes in the Ross Sea. Totally 13 penguin ornithogenic sediment profiles were collected from Inexpressible Island, Ross Sea, and the Cd/P ratios were used as a proxy of MCDW intrusion, enabling to reconstruct the variability of MCDW intrusion into the Ross Sea during the past 6,000 years. During the intervals of ∼0.7–1.6 and ∼2.8–6.0 kyr BP, enhanced MCDW intrusion increased the heat supply which warmed the surface water and reduced the coastal sea ice concentration. By contrast, reduced MCDW intrusion during ∼1.6–2.8 kyr BP caused a decrease in the penguin population via restricting food supply and/or increasing sea ice concentration. Thus, changes in MCDW were responsible for driving millennial changes in sea ice and penguin population in the Ross Sea.

Increased Contribution of Circumpolar Deep Water Upwelling to Methylmercury in the Upper Ocean around Antarctica: Evidence from Mercury Isotopes in the Ornithogenic Sediments

“…The Ross Sea shelf is strongly affected by upwelling associated with the CDW intrusion. [19][20][21][22]32 It has been reported that the CDW has a high MeHg content, serving as an additional potential source of MeHg to coastal waters. 6,33,34 The results of model simulations also emphasize the significant role of upwelling in contributing to MeHg levels in the surface waters (0−100 m) of the Southern Ocean.…”

“…Both modern observations and paleoclimate proxies suggest that the Ross Sea shelf is strongly affected by CDW invasion. 19,54 Notably, it has been demonstrated that the Hg isotope composition in the Antarctic biological archives can serve as a valuable tracer for MeHg cycling in the Southern Ocean. 55,56 Here we study the Hg isotopies in an ornithogenic sedimentary profile (CB2) strongly influenced by Adeĺie penguin (Pygoscelis adeliae) activity at Cape Bird, Ross Island, Antarctica (Figure S1).…”

“…In the areas with shallow bathymetry on the continental shelf and slope, the bottom sediments may also release Hg into overlying water bodies through diffusion and advection . It is worth noting that the coastal shelf areas of Antarctica are substantially influenced by upwelling caused by the intrusion of Circumpolar Deep Water (CDW), − which may serve as a crucial source of Hg in the upper ocean surrounding Antarctica. Indeed, significant Hg fluxes associated with upwelling have been reported in the Pacific Ocean, − supplying substantial quantities of Hg to the upper water bodies.…”

“…The CDW is the most voluminous water mass in the Southern Ocean (volume fraction of ∼53%), with high heat content and rich nutrients, and its upwelling has a substantial impact on the Antarctic climate and the ecosystem of the Southern Ocean. ,− Observational evidence shows that the CDW in the Southern Ocean has relatively high levels of MeHg, ,, implying that the CDW upwelling may be an important source of MeHg in upper water bodies and lead to higher Hg accumulation in coastal marine food webs. On the other hand, the upwelling of nutrients caused by CDW invasions may promote microbial activity, further enhancing in situ methylation of Hg in the water column .…”

Seasonal habitat preference and foraging behaviour of post-moult Weddell seals in the western Ross Sea

“…Where mCDW upwells along the shelf break, sensible heat polynyas can also appear. The nutrients supplied by mCDW promote primary productivity in the Ross Sea which leads to the production of phytoplankton that supports many marine species, including silverfish, an important prey item for Weddell seals [ 82 – 84 ]. By December or January, the maximum phytoplankton growth rate is reached within the polynya and, at this point, the Ross Sea is the most productive region in the Southern Ocean [ 78 , 85 , 86 ].…”