Clark, P. U., He, F., Golledge, N. R., Mitrovica, J. X., Dutton, A., Hoffman, J. S., et al. (2020). Oceanic forcing of penultimate deglacial and last interglacial sea-level rise. Nature, 577(7792), 660–+.
Abstract: Sea-level histories during the two most recent deglacial-interglacial intervals show substantial differences(1-3) despite both periods undergoing similar changes in global mean temperature(4,5) and forcing from greenhouse gases(6). Although the last interglaciation (LIG) experienced stronger boreal summer insolation forcing than the present interglaciation(7), understanding why LIG global mean sea level may have been six to nine metres higher than today has proven particularly challenging(2). Extensive areas of polar ice sheets were grounded below sea level during both glacial and interglacial periods, with grounding lines and fringing ice shelves extending onto continental shelves(8). This suggests that oceanic forcing by subsurface warming may also have contributed to ice-sheet loss(9-12) analogous to ongoing changes in the Antarctic(13,14) and Greenland(15) ice sheets. Such forcing would have been especially effective during glacial periods, when the Atlantic Meridional Overturning Circulation (AMOC) experienced large variations on millennial timescales(16), with a reduction of the AMOC causing subsurface warming throughout much of the Atlantic basin(9,12,17). Here we show that greater subsurface warming induced by the longer period of reduced AMOC during the penultimate deglaciation can explain the more-rapid sea-level rise compared with the last deglaciation. This greater forcing also contributed to excess loss from the Greenland and Antarctic ice sheets during the LIG, causing global mean sea level to rise at least four metres above modern levels. When accounting for the combined influences of penultimate and LIG deglaciation on glacial isostatic adjustment, this excess loss of polar ice during the LIG can explain much of the relative sea level recorded by fossil coral reefs and speleothems at intermediate- and far-field sites.
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Drury, A. J., John, C. M., & Shevenell, A. E. (2016). Evaluating climatic response to external radiative forcing during the late Miocene to early Pliocene: New perspectives from eastern equatorial Pacific (IODP U1338) and North Atlantic (ODP 982) locations: Late Miocene-Early Pliocene Variability. Paleoceanography, 31(1), 167–184.
Abstract: Orbital-scale climate variability during the latest Miocene-early Pliocene is poorly understood due to a lack of high-resolution records spanning 8.0-3.5Ma, which resolve all orbital cycles. Assessing this variability improves understanding of how Earth's system sensitivity to insolation evolves and provides insight into the factors driving the Messinian Salinity Crisis (MSC) and the Late Miocene Carbon Isotope Shift (LMCIS). New high-resolution benthic foraminiferal Cibicidoides mundulus O-18 and C-13 records from equatorial Pacific International Ocean Drilling Program Site U1338 are correlated to North Atlantic Ocean Drilling Program Site 982 to obtain a global perspective. Four long-term benthic O-18 variations are identified: the Tortonian-Messinian, Miocene-Pliocene, and Early-Pliocene Oxygen Isotope Lows (8-7, 5.9-4.9, and 4.8-3.5Ma) and the Messinian Oxygen Isotope High (MOH; 7-5.9Ma). Obliquity-paced variability dominates throughout, except during the MOH. Eleven new orbital-scale isotopic stages are identified between 7.4 and 7.1Ma. Cryosphere and carbon cycle sensitivities, estimated from O-18 and C-13 variability, suggest a weak cryosphere-carbon cycle coupling. The MSC termination coincided with moderate cryosphere sensitivity and reduced global ice sheets. The LMCIS coincided with reduced carbon cycle sensitivity, suggesting a driving force independent of insolation changes. The response of the cryosphere and carbon cycle to obliquity forcing is established, defined as Earth System Response (ESR). Observations reveal that two late Miocene-early Pliocene climate states existed. The first is a prevailing dynamic state with moderate ESR and obliquity-driven Antarctic ice variations, associated with reduced global ice volumes. The second is a stable state, which occurred during the MOH, with reduced ESR and lower obliquity-driven variability, associated with expanded global ice volumes.
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Hertzberg, J. E., Lund, D. C., Schmittner, A., & Skrivanek, A. L. (2016). Evidence for a biological pump driver of atmospheric CO2 rise during Heinrich Stadial 1. Geophys. Res. Lett., 43(23), 12,242–12,251.
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Hertzberg, J. E., Schmidt, M. W., Bianchi, T. S., Smith, R. W., Shields, M. R., & Marcantonio, F. (2016). Comparison of eastern tropical Pacific TEX86 and Globigerinoides ruber Mg/Ca derived sea surface temperatures: Insights from the Holocene and Last Glacial Maximum. Earth and Planetary Science Letters, 434, 320–332.
Abstract: The use of the TEX86TEX86 temperature proxy has thus far come to differing results as to whether TEX86TEX86 temperatures are representative of surface or subsurface conditions. In addition, although TEX86TEX86 temperatures might reflect sea surface temperatures based on core-top (Holocene) values, this relationship might not hold further back in time. Here, we investigate the TEX86TEX86 temperature proxy by comparing TEX86TEX86 temperatures to Mg/Ca temperatures of multiple species of planktonic foraminifera for two sites in the eastern tropical Pacific (on the Cocos and Carnegie Ridges) across the Holocene and Last Glacial Maximum. Core-top and Holocene View the MathML sourceTEX86H temperatures at both study regions agree well, within error, with the Mg/Ca temperatures of Globigerinoides ruber , a surface dwelling planktonic foraminifera. However, during the Last Glacial Maximum, View the MathML sourceTEX86H temperatures are more representative of upper thermocline temperatures, and are offset from G. ruber Mg/Ca temperatures by 5.8 °C and 2.9 °C on the Cocos Ridge and Carnegie Ridge, respectively. This offset between proxies cannot be reconciled by using different TEX86TEX86 temperature calibrations, and instead, we suggest that the offset is due to a deeper export depth of GDGTs at the LGM. We also compare the degree of glacial cooling at both sites based on both temperature proxies, and find that View the MathML sourceTEX86H temperatures greatly overestimate glacial cooling, especially on the Cocos Ridge. This study has important implications for applying the TEX86TEX86 paleothermometer in the eastern tropical Pacific.
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Puerres,, Bernal,, Brenner,, Restrepo-Moreno,, & Kenney,. (2018). Sedimentary records of extreme wave events in the southwestern Caribbean. Geomorphology, 319, 103–116.
Abstract: High-energy events in the Caribbean Sea include hurricanes, tropical storms, cold fronts and tsunamis. El Rosario Archipelago, located on the Colombian Caribbean shelf (SW Caribbean) consists of a set of ancient and successive coralline formations, uplifted by tectonic and diapiric activity. We undertook an integrated analysis of instrumental climate records and sediment records from a beach ridge system, a reef lagoon and a mangrove lagoon in the Archipelago, to determine whether historical extreme weather events influenced the coastal geomorphology and reef sedimentation. Statistical analysis of historical extreme winds and waves was accomplished using ERA-Interim reanalysis data. Extreme sea-level events were identified with calibrated data from the nearest tide gauge. Sediments from the reef and mangrove lagoon were dated using 210Pb and 14C. Beach ridges were dated indirectly thorough their relationship with the closure of the mangrove lagoon. The eroding capacity of the historical extreme waves (i.e. maximum grain size that could be entrained by the orbital velocity of the waves) was compared with the grain sizes present in the deposits, and foraminifera species helped to determine the provenance of those deposits. Storms typically occur during the dry season associated with cold fronts. Foraminifera and coral fragments indicated that beach ridges were supplied with sediment that eroded from ancient terraces. In the reef lagoon, a 56-cm-thick unit of coarse coral and shell debris, grading to a finer sediment, represents a major high-energy event that occurred after ca. 1655 CE. This event was also recorded by the beach ridges. The probable explanation for this high energy unit is that a strong event carried coarse sediments into the lagoon, with subsequent reworking by minor events, such as those reported in the historical record. Two tsunamis occurred in the Caribbean after 1655, but the associated waves reaching the area were not strong enough to deposit the coarser clasts of the unit. Thus, coarser material was probably delivered to the lagoon as a consequence of sudden diapiric and/or tectonic activity. Our data show that major storms and other high-wind, extreme-wave events shape the beach ridges on Rosario Island, every 70 years. The findings suggest that if global climate change increases the frequency and/or magnitude of major storms and other high-wind, extreme wave events that impact the Caribbean coast of Colombia, then El Rosario Archipelago will be susceptible to future, significant landscape transformations.
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