High-latitude biomes and rock weathering mediate climate–carbon cycle feedbacks on eccentricity timescales

Abstract

The International Ocean Discovery Programme (IODP) and its predecessors generated a treasure trove of Cenozoic climate and carbon cycle dynamics. Yet, it remains unclear how climate and carbon cycle interacted under changing geologic boundary conditions. Here, we present the carbon isotope (δ13C) megasplice, documenting deep-ocean δ13C evolution since 35 million years ago (Ma). We juxtapose the δ13C megasplice with its δ18O counterpart and determine their phase-difference on ~100-kyr eccentricity timescales. This analysis reveals that 2.4-Myr eccentricity cycles modulate the δ13C-δ18O phase relationship throughout the Oligo-Miocene (34-6 Ma), potentially through changes in continental weathering. At 6 Ma, a striking switch from in-phase to anti-phase behaviour occurs, signalling a reorganization of the climate-carbon cycle system. We hypothesize that this transition is consistent with Arctic cooling: Prior to 6 Ma, low-latitude continental carbon reservoirs expanded during astronomically-forced cool spells. After 6 Ma, however, continental carbon reservoirs contract rather than expand during cold periods due to competing effects between Arctic biomes (ice, tundra, taiga). We conclude that, on geologic timescales, System Earth experienced state-dependent modes of climate–carbon cycle interaction.

Mineral Dust Coupled With Climate‐Carbon Cycle on Orbital Timescales Over the Past 4 Ma

“…Furthermore, spring sea ice in the central Arctic Ocean reconstructed from IP 25 (a highly branched isopreneoid with 25 carbons) and summer sea surface temperature in the Arctic ocean obtained from long-chain alkenones revealed a seasonal sea ice cover with an ice-free summer season during the late Miocene in the central Arctic Ocean (Stein et al, 2016). Thus, an anti-phase relationship between δ 18 O benthic and δ 13 C benthic on the ∼100 kyr eccentricity scale after 6 Ma may be related to the establishment of a persistent and dynamic ice sheet in eastern Greenland and associated with changes of high-latitude biomes (De Vleeschouwer et al, 2020). Crucially, cooling in the Northern Hemisphere would expand arid areas and increase of dust fluxes because it would reduce the amount of water vapor in the atmosphere (e.g., Ding et al, 2002;Zhang et al, 2018), and this may also play a role in modulating the carbon and oxygen cycles.…”

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Deep-sea benthic foraminifera carbon isotopes (δ 13 C benthic ) reflect the dissolved inorganic carbon composition (δ 13 C DIC ) of the surrounding water column during calcification (e.g., De Vleeschouwer et al, 2020). On orbital time scales (10 4 -10 7 years), δ 13 C benthic is controlled by multiple factors.

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A ∼12 Myr Miocene Record of East Asian Monsoon Variability From the South China Sea

“…The Site 1146 chronology over the interval 12.8-5 Ma is based on minimal tuning of the benthic foraminiferal δ 18 O record to the orbital solution of Laskar et al (2004), using 48 age tie points along the revised sediment splice between Holes 1146A and 1146C (Table S1 and Figure 2). Modifications of the splice led to minor revisions of the age models in Holbourn et al (2018) and De Vleeschouwer et al (2020), which were both based on the splice version published in Holbourn et al (2018). Revision of the chronology between ∼17.3 and 12.7 Ma, based on correlation to the benthic foraminiferal isotope record of Site 1146 to the composite records of Integrated Ocean Drilling Program (IODP) Sites U1338 and U1337 in the eastern equatorial Pacific Ocean (Holbourn et al, 2014(Holbourn et al, , 2015(Holbourn et al, , 2020Kochhann et al, 2016), resulted in minor adjustments between ∼15.8 and 12.7 Ma.…”

Secular and orbital-scale variability of equatorial Indian Ocean summer monsoon winds during the late Miocene

“…S3b). 405-kyr modulation of the ocean carbon cycle, primarily recorded in carbonate content and benthic δ 13 C records (Herbert, 1997;Drury et al, 2020;De Vleeschouwer et al, 2020;Westerhold et al, 2020;Pälike et al, 2012;640 Paillard, 2017;Holbourn et al, 2007) but also in productivity and monsoon-related dust records (Rickaby et al, 2007;Wang et al, 2010), has been observed throughout the Cenozoic and Mesozoic sedimentary record. In middle Miocene records, poor carbonate preservation noted during eccentricity maxima is interpreted as indicating transient shoaling of the carbonate compensation depth (Holbourn et al, 2007;Flower and Kennett, 1994).…”