Publication Date:
2022-05-26
Description:
Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography and Paleoclimatology, 34, (2019): 2141-2157, doi: 10.1029/2019PA003731.
Description:
Dissolution of calcite in deep ocean sediments, which is required to balance global marine CaCO3 production and burial fluxes, is still a poorly understood process. In order to assess the mechanisms of dissolution in sediments, we analyzed four multicore tops taken along a depth transect on the Ontong‐Java Plateau. These cores were taken directly on the equator, and span water column calcite saturation states from ∼0.93 to ∼0.74, allowing us to assess the effect of dissolution on carbonate sediment composition. The top 2 cm of each multicore was sectioned and sieved to separate coccolith from foraminiferal calcite, and the %CaCO3, δ13C, Δ14C, and Mg/Ca were evaluated. The mass ratio of coccoliths to foraminifera increases by a factor of 3 as a function of water depth, reflecting the preferential dissolution of foraminifera. Carbon isotope (δ13C and Δ14C) data suggest that most dissolution takes place at the sediment‐water interface and primarily affects foraminifera. Mg/Ca analyses indicate that the Mg content of the entire foraminiferal assemblage decreases as a function of dissolution. In contrast, coccolith dissolution takes place within the sediments, rather than at the interface. Together these two processes cause coccoliths to be up to 1,000 radiocarbon years younger than foraminifera from the same depth horizon. Despite this within‐sediment coccolith dissolution flux, sediments below the calcite saturation horizon remain enriched in coccolith calcite. Combined with global seafloor hypsometry and calcium carbonate content, this enrichment suggests that globally, coccoliths may outweigh foraminifera in deep ocean sediments by a factor of 1.8.
Description:
A. V. S. thanks the NOSAMS facility and the WHOI/NOSAMS postdoc scholar program, James Funds, and the Bessette family for funding and support. A. Q. acknowledges Williams College research and travel funds. We thank the Stanley W. Watson Director's Discretionary Fund for the Picarro‐Automate analyzer. We thank Ellen Roosen at the WHOI core repository for help with sample identification and sectioning. Thanks to Gretchen Swarr and the WHOI plasma mass spectrometry facility. Finally, we thank Bill Martin and Wally Broecker for enlightening discussions on dissolution and radiocarbon dating of deep ocean sediments. All data are included as supporting information files and are archived with NOAA's World Data Service for Paleoceanography (WDS Paleo; https://www.ncdc.noaa.gov/paleo/study/28150).
Description:
2020-05-15
Repository Name:
Woods Hole Open Access Server
Type:
Article
