North Atlantic marine biogenic silica accumulation through the early-to-mid Paleogene: implications for ocean circulation and silicate weathering feedback

• Main Authors: Witkowski, Jakub, Bryłka, Karolina, Bohaty, Steven M., Mydłowska, Elżbieta, Penman, Donald E., Wade, Bridget S.
• Format: Text
• Language: English
• Published: 2021
• Subjects: Greenland; Pacific; Greenland Sea; North Atlantic
• Online Access: https://doi.org/10.5194/cp-2021-50; https://cp.copernicus.org/preprints/cp-2021-50/

The Paleogene history of biogenic opal accumulation in the North Atlantic provides insight into both the evolution of deep-water circulation in the Atlantic basin, and weathering responses to major climate shifts. However, existing records are compromised by low temporal resolution and/or stratigraphic discontinuities. In order to address this problem, we present a multi-site, high-resolution record of biogenic silica ( bio SiO 2 ) accumulation from Blake Nose (ODP Leg 171B, western North Atlantic) spanning the early Paleocene through late Eocene time interval (~65‒34 Ma). This record represents the longest single-locality history of marine bio SiO 2 burial compiled to date and offers a unique perspective into changes in bio SiO 2 fluxes through the early-to-mid Paleogene extreme greenhouse interval and subsequent period of long-term cooling. Blake Nose bio SiO 2 fluxes display prominent fluctuations that we attribute to variations in sub-thermocline nutrient supply via cyclonic eddies associated with the Gulf Stream. Whereas few constraints are available on the bio SiO 2 flux pulses peaking in the early Paleocene and early Eocene, a middle Eocene interval of elevated bio SiO 2 flux between ~46 and 42 Ma is proposed to reflect nutrient enrichment due to invigorated overturning circulation following an early onset of Northern Component Water export from the Norwegian-Greenland Sea at ~49 Ma. Comparison of our North Atlantic record against published Pacific bio SiO 2 flux records indicates a diminished nutrient supply to the Atlantic between ~42 and 38 Ma, interpreted as a response to weakening of the overturning circulation. Subsequently, a deep-water circulation regime favoring limited bio SiO 2 burial in Atlantic and enhanced bio SiO 2 burial in the Pacific was established after ~38 Ma, likely in association with a further invigoration of deep-water export from the North Atlantic. We also observe that Blake Nose bio SiO 2 fluxes through the middle Eocene cooling interval (~48 to 34 Ma) are consistently higher than background fluxes throughout the late Paleocene‒early Eocene interval of intense greenhouse warmth. This observation is consistent with a temporally variable rather than constant silicate weathering feedback strength model for the Paleogene, which would instead predict that marine bio SiO 2 burial should peak during periods of extreme warming.