(Table 1) Alkenone concentration, UK'37 index and derived sea surface temperatures for ODP Site 167-1020

Uk'37 sea-surface temperature (SST) estimates obtained at ~2.5-k.y. resolution from Ocean Drilling Program Site 1020 show glacial-interglacial cyclicity with an amplitude of 7°-10°C over the last 780 k.y. This record shows a similar pattern of variability to another alkenone-based SST record obtained previously from the Santa Barbara Basin. Both records show that oxygen isotope Stage (OIS) 5.5 was warmer by ~3°C relative to the present and that glacial Uk'37 temperatures warm in advance of deglaciation, as inferred from benthic d18O records. The alkenone-based SST record at Site 1020 is longer than previously published work along the California margin. We show that warmer than present interglacial stages have occurred frequently during the last 800 k.y. Alkenone concentrations, a proxy for coccolithophorid productivity, indicate that sedimentary marine organic carbon content has also varied significantly over this interval, with higher contents during interglacial periods. A baseline shift to warmer SST and greater alkenone content occurs before OIS 13.
We compare our results with those from previous multiproxy studies in this region and conclude that SST has increased by ~5°C since the last glacial period (21 ka). Our data show that maximum alkenone SSTs occur simultaneously with minimum ice volume at Site 1020, which is consistent with data from farther south along the margin. The presence of sea ice in the glacial northeast Pacific, the extent of which is inferred from locations of ice-rafted debris, provides further support for our notion of cold surface water within the northern California Current system, averaging 7°-8°C cooler during peak glacial conditions. The cooling of surface water during glacial stages most likely did not result from enhanced upwelling because alkenone concentrations and terrestrial redwood pollen assemblages are consistently lower during glacial periods.

基于大洋钻探计划（Ocean Drilling Program, ODP）1020站位获取的分辨率约2.5千年的Uk'37海表温度（sea-surface temperature, SST）估算结果显示，过去78万年间存在振幅达7℃至10℃的冰期-间冰期旋回特征。该记录与此前从圣巴巴拉盆地获取的另一项基于烯酮（alkenone）的海表温度记录具有相似的变化模式。两项记录均表明，氧同位素阶段（oxygen isotope Stage, OIS）5.5较现代偏暖约3℃；且根据底栖δ18O记录推断，冰期Uk'37海表温度在冰消作用之前便已开始升温。1020站位的基于烯酮的海表温度记录，长度长于此前沿加利福尼亚边缘海域发表的相关研究成果。本研究证实，过去80万年间频繁出现过较现代偏暖的间冰期阶段。作为颗石藻（coccolithophorid）生产力代用指标的烯酮浓度显示，该时段内沉积海相有机碳含量同样存在显著波动，且间冰期阶段含量更高。在氧同位素阶段13之前，海表温度与烯酮含量均出现向暖态的基准偏移。
本研究将所得结果与该区域此前的多代用指标研究结果进行对比后得出结论：自末次冰期（21 ka）以来，海表温度已升高约5℃。数据显示，1020站位的烯酮基海表温度峰值与冰量最小值同步出现，这与加利福尼亚边缘海域更南部区域的观测数据一致。根据浮冰碎屑（ice-rafted debris）分布推断的冰川期东北太平洋海冰存在情况，进一步佐证了北加利福尼亚海流系统内存在冷水表层水的结论——冰盛期时该区域表层水温平均偏低7℃至8℃。冰期阶段的表层海水降温大概率并非由上升流增强所致，因为冰期期间烯酮浓度与陆地红杉花粉组合均持续处于较低水平。