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Ongoing Increase in Eastern Tropical North Pacific Denitrification as Interpreted Through the Santa Barbara Basin Sedimentary δ 15 N Record
Author(s) -
Davis C. V.,
OntiverosCuadras J. F.,
BenitezNelson C.,
Schmittner A.,
Tappa E. J.,
Osborne E.,
Thunell R. C.
Publication year - 2019
Publication title -
paleoceanography and paleoclimatology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.927
H-Index - 127
eISSN - 2572-4525
pISSN - 2572-4517
DOI - 10.1029/2019pa003578
Subject(s) - oceanography , sedimentary rock , geology , sediment , ocean gyre , biogeochemical cycle , structural basin , sediment trap , estuary , climatology , environmental science , subtropics , water column , geochemistry , paleontology , ecology , biology
Decades of observations show that the world's oceans have been losing oxygen, with far‐reaching consequences for ecosystems and biogeochemical cycling. To reconstruct oxygenation beyond the limited scope of instrumental records, proxy records are needed, such as sedimentary δ 15 N. We combine two δ 15 N records from the Santa Barbara Basin (SBB), a 24‐year‐long, biweekly sediment trap time series, and a 114‐year, high‐resolution sediment core together spanning the years 1892–2017. These records allow for the examination of δ 15 N variability on seasonal to centennial timescales. Seasonal variability in SBB δ 15 N is consistent in timing with the poleward advection of a high δ 15 N signal from the Eastern Tropical North Pacific in the summer and fall. Strong El Niño events result in variable δ 15 N signatures, reflective of local rainfall, and neither the Pacific Decadal Oscillation nor North Pacific Gyre Oscillation impose strong controls on bulk sedimentary δ 15 N. Seasonal and interannual variability in sediment trap δ 13 C org is consistent with local productivity as a driver; however, this signal is not retained in the sediment core. The time series from the sediment trap and core show that bulk sedimentary δ 15 N in SBB has now exceeded that measured for the past 2,000 years. We hypothesize that the change in δ 15 N reflects the increasing influence of denitrified waters from the Eastern Tropical North Pacific and ongoing deoxygenation of the Eastern Pacific. When juxtaposed with other regional δ 15 N records our results further suggest that SBB is uniquely situated to record long‐term change in the Eastern Tropical North Pacific.