Interactions Between Water Masses and Carbonate Preservation in the Ross Sea: Evidence from Foraminiferal and Microtektite Distribution

The Ross Sea is a globally significant annual atmospheric CO2 sink and hosts the largest phytoplankton bloom. It is characterized by a shallow carbonate compensation depth (CCD) and crucial water mass transformations. This study investigates the distribution of calcareous foraminifera and microtektites to evaluate carbonate preservation in surface sediments approximately 0.8 million years old.

In the western Ross Sea (WRS), pale-yellow microtektites originating from northern Victoria Land are distributed along the pathway of cold shelf water (SW), influenced by terrestrial input from the Victoria Land shelf. Calcareous benthic and pelagic foraminifera dominate in the central and eastern Ross Sea (CRS and ERS), following the pathways of warm Modified Circumpolar Deep Water (MCDW) and/or Circumpolar Deep Water (CDW). Surface sediments in these regions contain few diatoms and a higher proportion of >125 μm sediment fractions.

In the CRS, foraminiferal assemblages are dominated by Trifarina earlandi, with common occurrences of Ehrenbergina glabra, Globocassidulina biora, and Cibicides spp., along with abundant Neogloboquadrina pachyderma. In the ERS, G. biora dominates, accompanied by E. glabra and N. pachyderma. The Ross Sea’s shallow CCD, ranging from 350–400 m to 500–550 m, coexists with calcareous foraminiferal assemblages in sediments at depths of 400–600 m, suggesting that CCD depth is not the primary factor governing carbonate preservation.

The distribution of calcareous foraminifera aligns with water current pathways, highlighting water temperature as the key determinant of their survival. The temperature of MCDW, modulated by mixing with cold SW, plays a critical role in carbonate preservation.