Roles of insolation forcing and CO2 forcing on Late Pleistocene seasonal sea surface temperatures

Abstract

Late Pleistocene changes in insolation, greenhouse gas concentrations, and ice sheets have different spatially and seasonally modulated climatic fingerprints. By exploring the seasonality of paleoclimate proxy data, we gain deeper insight into the drivers of climate changes. Here, we investigate changes in alkenone-based annual mean and Globigerinoides ruber Mg/Ca-based summer sea surface temperatures in the East China Sea and their linkages to climate forcing over the past 400,000 years. During interglacial-glacial cycles, there are phase differences between annual mean and seasonal (summer and winter) temperatures, which relate to seasonal insolation changes. These phase differences are most evident during interglacials. During glacial terminations, temperature changes were strongly affected by CO2. Early temperature minima, ~20,000 years before glacial terminations, except the last glacial period, coincide with the largest temperature differences between summer and winter, and with the timing of the lowest atmospheric CO2 concentration. These findings imply the need to consider proxy seasonality and seasonal climate variability to estimate climate sensitivity.

Long-chain alkenones in the Shimosa Group reveal palaeotemperatures of the Pleistocene interglacial Palaeo-Tokyo Bays

“…Our results suggest that MIS 9 seems to be the warmest interglacial since the mid-Brunhes event. These tendencies are comparable to the temperature records from cores U1429 and C9001 (Phillips and Harwood 2017;Lee et al 2021), the CO 2 record in Fig. 5 Results of LCA concentration and U K ′ 37 -SST.…”

“…These temperatures are 2-3 ℃ higher than the U K ′ 37 -SSTs of the pre-industrial level of Tokyo Bay recovered from the sediment core KT12-06-2B (Kajita et al 2020b) and possibly equivalent to or warmer than the values of the Holocene thermal maximum (5-7 ka), which was previously estimated to be approximately 2 ℃ higher than that of the pre-industrial level (Matsushima and Ohshima 1974;Matsushima 1979). High temperatures in MIS 5e compared to the present level have also been recorded in several cores (MD01-2421, MR97-04-1, MR99-04-2, MR00-05-2, MR02-03-2) collected from the Kuroshio-Oyashio mixing zone (Yamamoto et al 2004;Koizumi and Yamamoto 2010), the core from site U1429 in the East China Sea under the influence of the branched Kuroshio Current (Lee et al 2021), and the core from site C9001 off the northern Honshu coastal region under the influence of the Oyashio Current (Phillips and Harwood 2017). In the high latitudes of the Northern Hemisphere, not only in the Pacific Ocean but also globally, 1-2 ℃ warmer SSTs than the pre-industrial level have been recorded for the peak of MIS 5e, which are considered to have been caused by high summer insolation and positive feedback related to ice distributions (Hoffman et al 2017;Thomas et al 2020;Turney et al 2020).…”

Comparison and Synthesis of Sea‐Level and Deep‐Sea Temperature Variations Over the Past 40 Million Years

“…The linear relationship assumed in the inverse modeling approach between deep‐sea δ c (through temperature) and Northern Hemisphere high‐latitude temperature seems to be at odds with consistently low deep‐sea temperature with muted variability, punctuated by sharp warm anomalies at peak interglacials (Bates et al., 2014; Cutler et al., 2003; Elderfield et al., 2012; Rohling et al., 2021; Siddall et al., 2010). This Late Pleistocene signal structure in deep‐sea temperature is more reminiscent of Antarctic ice‐core and southern high‐latitude temperature time series than Greenland, North Atlantic, or North Pacific temperature time series (e.g., Hasenfratz et al., 2019; K. E. Lee et al., 2021; Rodrigues et al., 2017; Rohling et al., 2012, 2021), with similar or shorter time scale variations over the last glacial cycle (Anderson et al., 2021). It is striking that this dominance of southern high‐latitude variability in global deep‐sea temperature variations is so apparent in the Late Pleistocene, when ice‐ages were distinctly dominated by Northern Hemisphere ice‐sheet waxing and waning.…”

Comparison and synthesis of sea-level and deep-sea temperature variations over the past 40 million years

“…The linear relationship assumed in the inverse modeling approach between deep-sea δc (through temperature) and Northern Hemisphere high-latitude temperature seems to be at odds with consistently low deep-sea temperature with muted variability, punctuated by sharp warm anomalies at peak interglacials (Cutler et al, 2003;Elderfield et al, 2012;Siddall et al, 2010;Bates et al, 2014;Rohling et al, 2021). This Late Pleistocene signal structure in deep-sea temperature is more reminiscent of Antarctic ice-core and southern high-latitude temperature time series than Greenland, North Atlantic, or North Pacific temperature time series (e.g., Rohling et al, 2012Rohling et al, , 2021Rodrigues et al, 2017;Hasenfratz et al, 2019;Lee et al, 2021), with similar or shorter time scale variations over the last glacial cycle (Anderson et al, 2021). It is striking that this dominance of southern high-latitude variability in global deep-sea temperature variations is so apparent in the Late Pleistocene, when ice-ages were distinctly dominated by Northern Hemisphere ice-sheet waxing and waning.…”