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1. Miocene Evolution of North Atlantic Sea Surface Temperature

   https://doi.org/10.1029/2019PA003748  

   Super, James_R ; Thomas, Ellen ; Pagani, Mark ; Huber, Matthew ; O'Brien, Charlotte_L ; Hull, Pincelli_M ( May 2020 , Paleoceanography and Paleoclimatology)

   We reconstruct sea surface temperatures (SSTs) at Deep Sea Drilling Project Site 608 (42.836°N, 23.087°), north of the Azores Front, and Ocean Drilling Program Site 982 (57.516°N, 15.866°), under the North Atlantic Current, in order to track Miocene (23.1–5.3 Ma) development of North Atlantic surface waters. Mean annual SSTs from TEX₈₆and U^K′₃₇proxy estimates at both sites were 10–15 °C higher than modern through the Miocene Climatic Optimum (17–14.5 Ma). During the global cooling of the Middle Miocene Climate Transition (~14.5–12.5 Ma), SSTs at midlatitude Site 608 cooled by ~6 °C, whereas high‐latitude Site 982 cooled by only ~2 °C, resulting in an ~4 Myr collapse of the SST gradient between the two sites. This regional pattern is inconsistent with an increased latitudinal surface temperature gradient, as generally associated with global cooling episodes linked to decreasingpCO₂levels. Instead, the pattern is best explained by enhanced ocean heat transport into the high‐latitude North Atlantic superimposed on the global cooling trend, probably due to enhanced Atlantic meridional overturning circulation and/or a stronger North Atlantic Current. During global late Miocene cooling (~8–7 Ma), surface waters cooled by ~6 °C at Site 982 while minimal change occurred at Site 608, reestablishing the North Atlantic SST gradient. The collapse and reemergence of the SST gradient between the middle‐ and high‐latitude North Atlantic suggests that interaction between changes in regional ocean circulation and the global response to changes in greenhouse gas concentration was important in Miocene climate evolution.

    

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2. Latitudinal Variance in the Drivers and Pacing of Warmth During Mid‐Pleistocene MIS 31 in the Antarctic Zone of the Southern Ocean

   https://doi.org/10.1029/2021PA004394  

   Warnock, Jonathan P. ; Reilly, Brendan T. ; Raymo, Maureen E. ; Weber, Michael E. ; Peck, Victoria ; Williams, Trevor ; Armbrecht, Linda ; Bailey, Ian ; Brachfeld, Stefanie ; Du, Zhiheng ; et al ( August 2022 , Paleoceanography and Paleoclimatology)

   Early Pleistocene Marine Isotope Stage (MIS)‐31 (1.081–1.062 Ma) is a unique interval of extreme global warming, including evidence of a West Antarctic Ice Sheet (WAIS) collapse. Here we present a new 1,000‐year resolution, spanning 1.110–1.030 Ma, diatom‐based reconstruction of primary productivity, relative sea surface temperature changes, sea‐ice proximity/open ocean conditions and diatom species absolute abundances during MIS‐31, from the Scotia Sea (59°S) using deep‐sea sediments collected during International Ocean Discovery Program (IODP) Expedition 382. The lower Jaramillo magnetic reversal (base of C1r.1n, 1.071 Ma) provides a robust and independent time‐stratigraphic marker to correlate records from other drill cores in the Antarctic Zone of the Southern Ocean (AZSO). An increase in open ocean speciesFragilariopsis kerguelensisin early MIS‐31 at 53°S (Ocean Drilling Program Site 1,094) correlates with increased obliquity forcing, whereas at 59°S (IODP Site U1537; this study) three progressively increasing, successive peaks in the relative abundance ofF. kerguelensiscorrelate with Southern Hemisphere‐phased precession pacing. These observations reveal a complex pattern of ocean temperature change and sustained sea surface temperature increase lasting longer than a precession cycle within the Atlantic sector of the AZSO. Timing of an inferred WAIS collapse is consistent with delayed warmth (possibly driven by sea‐ice dynamics) in the southern AZSO, supporting models that indicate WAIS sensitivity to local sub‐ice shelf melting. Anthropogenically enhanced impingement of relatively warm water beneath the ice shelves today highlights the importance of understanding dynamic responses of the WAIS during MIS‐31, a warmer than Holocene interglacial.

    

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3. The Role of the Greenland-Scotland Ridge in Step-wise Cooling of the Nordic Seas from the Middle to Late Miocene

   O'Mara, N. A. ; Polissar, P. J. ; Uno, K. T. ; Phelps, S. R. ; Buzeta, R. K. ; deMenocal, P. B. ( December 2018 , American Geophysical Union, Fall Meeting 2018, abstract #PP13E-1364)

   Neogene ocean temperatures are characterized by sustained warmth during the mid-Miocene Climatic Optimum followed by gradual cooling through the late Miocene culminating in Northern Hemisphere glaciation in the early Pleistocene. While the magnitude of sea surface temperature (SST) cooling is enhanced at higher latitudes, existing records suggest that the timing is nearly synchronous across the world's oceans. However, the Nordic Seas, north of the Greenland-Scotland Ridge (GSR), experienced rapid cooling steps (14.5-14 Ma, 12.5-12 Ma, 8-6 Ma) that are out of sync with the global SST cooling trend. Here we present a new alkenone paleo-SST record from Ocean Drilling Program (ODP) site 985 in the western Norwegian Sea (66°56' N, 6°27' W) and investigate the relationships between rapid SST change, depth of the GSR, ocean circulation, and deep-water formation using proxy and model data. We find significant (p < 0.01) inverse relationships between the depth of the GSR and SSTs at ODP sites north of the ridge (985 and 907), positive relationships between GSR depth and the SST gradient across the ridge, and inverse relationships between deep water production and SST at ODP sites 985 and 907. In sum, these observations suggest that during global Miocene cooling, intervals of GSR deepening allowed for increased sea water exchange and an invigoration of deep-water production in the North Atlantic. We posit that enhanced surficial cyclonic flow in the Nordic Seas and a strengthened East Greenland Current caused rapid cooling in the western Nordic Seas. This cooling is consistent with Pliocene coupled climate model runs with altered tectonic boundary conditions simulating a deeper GSR, implying that this SST response to changes to GSR depth may be an important mechanism in high latitude Neogene climate. Furthermore, a strong linear relationship (r2 = 0.84) between ODP 985 SST and global deep ocean δ13C suggests that ocean circulation responses to tectonically forced variability in the GSR may have had an important impact on the Neogene carbon cycle. 

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4. Subsurface Heat Channel Drove Sea Surface Warming in the High‐Latitude North Atlantic During the Mid‐Pleistocene Transition

   https://doi.org/10.1029/2020GL091899  

   Catunda, M. Carolina A. ; Bahr, André ; Kaboth‐Bahr, Stefanie ; Zhang, Xu ; Foukal, Nicholas P. ; Friedrich, Oliver ( June 2021 , Geophysical Research Letters)

   The Mid‐Pleistocene Transition (MPT, 1,200–600 ka) marks the rapid expansion of Northern Hemisphere (NH) continental ice sheets and stronger precession pacing of glacial/interglacial cyclicity. Here, we investigate the relationship between thermocline depth in the central North Atlantic, subsurface northward heat transport and the initiation of the 100‐kyr cyclicity during the MPT. To reconstruct deep‐thermocline temperatures, we generated a Mg/Ca‐based temperature record of deep‐dwelling (∼800 m) planktonic foraminifera from mid‐latitude North Atlantic at Site U1313. This record shows phases of pronounced heat accumulation at subsurface levels during the mid‐MPT glacial driven by increased outflow of the Mediterranean Sea. Concurrent warming of the subtropical thermocline and subpolar surface waters indicates enhanced (subsurface) inter‐gyre transport of warm water to the subpolar North Atlantic, which provided moisture for ice‐sheet growth. Precession‐modulated variability in the northward transport of subtropical waters imprinted this orbital cyclicity into NH ice‐sheets after Marine Isotope Stage 24.

    

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5. Obliquity Dominance in Early Pleistocene Sediments From the Antarctic Zone of the Southern Ocean (Indian Ocean Sector)

   https://doi.org/10.1029/2024PA004855  

   Billups, K. ; Münch, B. ; Garrioch, I. ; Bradtmiller, L. ( May 2024 , Paleoceanography and Paleoclimatology)

   We constructed a record of percent biogenic silica (opal) accumulation at Ocean Drilling Program Site 745B located in the Indian Ocean sector of the Antarctic Zone of the Southern Ocean. The record spans the majority of the early Pleistocene (1.1–2.6 Ma). Orbital‐scale sampling affords a look at the relative importance of obliquity versus precession variability through a time interval that is characterized by obliquity pacing in early Pleistocene δ¹⁸O records. Variations in the site's magnetic susceptibility record closely resemble those in the benthic foraminiferal δ¹⁸O stack (Lisiecki & Raymo, 2005,https://doi.org/10.1029/2004pa001071) and provide orbital‐scale age control. Between 1.1 and 1.8 Ma, obliquity‐related 41 kyr spectral peaks dominate with relatively little power at precession periods (23–19 kyr) in all records. Between 1.8 and 2.6 Ma, only the δ¹⁸O and magnetic susceptibility data display a distinct 41 kyr peak, while the opal lacks spectral power at any of the orbital periodicities. The lack of more pronounced precession‐scale variations in the two proxy records is consistent with observations in foraminiferal δ¹⁸O records. A low or absent response to precession in these records appears to be due to environmental control. Lack of orbital forcing in the opal record before 1.8 Ma may reflect both a more southerly location of the polar frontal zone with respect to the site, and thus the site's position outside the region of wind‐driven upwelling, and/or upwelling waters undersaturated with respect to silica prior to the establishment of the opal belt at about 2 Ma.

    

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