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

• Main Authors: J. Witkowski, K. Bryłka, S. M. Bohaty, E. Mydłowska, D. E. Penman, B. S. Wade
• Format: Article
• Language: English
• Published: Copernicus Publications 2021-09-01
• Series: Climate of the Past
• Online Access: https://cp.copernicus.org/articles/17/1937/2021/cp-17-1937-2021.pdf
• ISSN: 1814-9324; 1814-9332

<p>The Paleogene history of biogenic opal accumulation in the North Atlantic provides insight into both the evolution of deepwater 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 (<span class="inline-formula">_bioSiO₂</span>) accumulation from Blake Nose (ODP Leg 171B, western North Atlantic) spanning the early Paleocene to late Eocene time interval (<span class="inline-formula">∼65</span>–34 Ma). This record represents the longest single-locality history of marine <span class="inline-formula">_bioSiO₂</span> burial compiled to date and offers a unique perspective into changes in <span class="inline-formula">_bioSiO₂</span> fluxes through the early to middle Paleogene extreme greenhouse interval and the subsequent period of long-term cooling. Blake Nose <span class="inline-formula">_bioSiO₂</span> fluxes display prominent fluctuations that we attribute to variations in sub-thermocline nutrient supply via cyclonic eddies associated with the Gulf Stream. Following elevated and pulsed <span class="inline-formula">_bioSiO₂</span> accumulation through the Paleocene to early Eocene greenhouse interval, a prolonged interval of markedly elevated <span class="inline-formula">_bioSiO₂</span> flux in the middle Eocene between <span class="inline-formula">∼46</span> and 42 Ma is proposed to reflect nutrient enrichment at Blake Nose due to invigorated overturning circulation following an early onset of Northern Component Water export from the Norwegian–Greenland Sea at <span class="inline-formula">∼49</span> Ma. Reduced <span class="inline-formula">_bioSiO₂</span> flux in the North Atlantic, in combination with increased <span class="inline-formula">_bioSiO₂</span> flux documented in existing records from the equatorial Pacific between <span class="inline-formula">∼42</span> and 38 Ma, is interpreted to indicate diminished nutrient supply and reduced biosiliceous productivity at Blake Nose in response to weakening of the overturning circulation. Subsequently, in the late Eocene, a deepwater circulation regime favoring limited <span class="inline-formula">_bioSiO₂</span> burial in the Atlantic and enhanced <span class="inline-formula">_bioSiO₂</span> burial in the Pacific was established after <span class="inline-formula">∼38</span> Ma, likely in conjunction with re-invigoration of deepwater export from the North Atlantic. We also observe that Blake Nose <span class="inline-formula">_bioSiO₂</span> fluxes through the middle Eocene cooling interval (<span class="inline-formula">∼48</span> to 34 Ma) are similar to or higher than background fluxes throughout the late Paleocene–early Eocene interval (<span class="inline-formula">∼65</span> to 48 Ma) 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 <span class="inline-formula">_bioSiO₂</span> burial should peak during periods of extreme warming.</p>