Causes of ice age intensification across the Mid-Pleistocene Transition

Abstract

SignificanceConflicting sets of hypotheses highlight either the role of ice sheets or atmospheric carbon dioxide (CO2) in causing the increase in duration and severity of ice age cycles ∼1 Mya during the Mid-Pleistocene Transition (MPT). We document early MPT CO2 cycles that were smaller than during recent ice age cycles. Using model simulations, we attribute this to post-MPT increase in glacial-stage dustiness and its effect on Southern Ocean productivity. Detailed analysis reveals the importance of CO2 climate forcing as a powerful positive feedback that magnified MPT climate change originally triggered by a change in ice sheet dynamics. These findings offer insights into the close coupling of climate, oceans, and ice sheets within the Earth System.

A Cool, Nutrient‐Enriched Eastern Equatorial Pacific During the Mid‐Pleistocene Transition

“…More importantly for the global air-sea CO 2 balance (Marinov et al, 2006;Sigman et al, 2010), the inference of higher nutrient supply to the low latitudes suggests that the biological pump south of the Polar Front was relatively weak during the MPT. The decrease in nutrient supply to low latitudes suggests that nutrient drawdown in the polar Antarctic ramped up across the MPT, consistent with the inferred Fe fertilization of the post-MPT polar oceans (Chalk et al, 2017). The decrease in nutrient supply to low latitudes suggests that nutrient drawdown in the polar Antarctic ramped up across the MPT, consistent with the inferred Fe fertilization of the post-MPT polar oceans (Chalk et al, 2017).…”

“…During the MPT, the weak nutrient consumption implied by the δ 15 N records presented here suggests that despite high biogenic silica burial, the EEP was a local source of CO 2 to the atmosphere. After the MPT, the reduction in pCO 2 is attributed to an enhanced Southern Ocean biological pump stimulated by enhanced Fe availability as a result of the increased aridity and dustiness of the atmosphere (Chalk et al, 2017;Martinez-Garcia et al, 2011). After the MPT, the reduction in pCO 2 is attributed to an enhanced Southern Ocean biological pump stimulated by enhanced Fe availability as a result of the increased aridity and dustiness of the atmosphere (Chalk et al, 2017;Martinez-Garcia et al, 2011).…”

Expedition 383 Prospectus: Dynamics of the Pacific Antarctic Circumpolar Current (DYNAPACC)

“…Martinez-Garcia et al (2009, 2014 suggested that around 40-50 parts per million by volume (ppmv) of the glacial atmospheric CO 2 decline can be attributed to iron fertilization ( Figure F10), which is in good agreement with model estimates Chalk et al, 2017;Brovkin et al, 2007). At ODP Site 1090, the first significant rise in ice age dust and iron deposition over the past 4 My occurred at ~2.7 Ma, whereas the most dramatic rise in dust deposition occurred across the mid-Pleistocene transition (Martínez-García et al, 2011).…”

Spratlies Archipelago as the Australasian Tektite Impact Crater, Details of Formation & Richard Muller’s Dust Cloud Explanation for the Mid-Pleistocene Ice Age Cycle Transition

“…The same effect is routinely observed in calm nights when there is zero H 2 O vapor in the air. Also again, the date of 1 Ma reported for the ice age cycle upheaval in the PNAS article [8] is too early.…”

“…(Nov. 2017), entitled "Causes of ice age intensification across the Mid-Pleistocene Transition" [8], is purporting to explain the change in ice age cycles as caused by CO 2 level variation.…”