At present, variations of primary productivity (PP) in the Bay of Bengal (BoB) are driven by salinity-related stratification, which is controlled by the Indian summer monsoon (ISM). The relationships between PP, precipitation, and more generally climate in the past are not clearly understood. Here, we present a new record of PP based on the examination of coccolithophore assemblages in a 26 000-year sedimentary series retrieved in the northeastern BoB (core MD77-176). We compare our PP records to published climate and monsoon records, as well as outputs from numerical experiments obtained with the Earth system model IPSL-CM5A-LR, including the marine biogeochemical component PISCES, and with the transient climate simulation TraCE-21. Our results show that PP was most probably controlled by nutrient contents and distribution within the upper water column, which were predominantly influenced by (i) regional river systems between 26 and 19 ka, i.e. when sea level was relatively low and climate was relatively dry, and (ii) salinity-related stratification over the last 19 kyr, i.e. when sea level rose and more humid conditions prevailed. During that period, salinity and stratification were directly related to monsoon precipitation dynamics, which were chiefly forced by both insolation and Atlantic meridional overturning circulation (AMOC) strength. During Heinrich Stadial 1 and the Younger Dryas, i.e. when the AMOC collapsed, weaker South Asian precipitation diminished stratification and enhanced PP. During Bølling–Allerød, i.e. when the AMOC recovered, stronger South Asian precipitation increased stratification and subdued PP. Similarly, the precipitation peak recorded around the middle–early Holocene is consistent with a stronger stratification that drives PP minima.

中文翻译：

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过去26000年孟加拉东北部湾的初级生产力动态

目前，孟加拉湾（BoB）的初级生产力（PP）的变化是由与盐度有关的分层驱动的，该分层受印度夏季风（ISM）控制。PP，降水和过去更普遍的气候之间的关系尚不清楚。在这里，我们根据对东北BoB（核心MD77-176）中26 000年沉积系列中的球石藻体组合的研究，提出了PP的新记录。我们将PP记录与已发布的气候和季风记录进行比较，并比较使用IPSL-CM5A-LR地球系统模型（包括海洋生物地球化学成分PISCES）和瞬时气候模拟TraCE-21获得的数值实验输出。我们的研究结果表明，PP最有可能受上部水域中养分含量和分布的控制，主要受（i）26至19 ka之间的区域河流系统的影响，即当海平面相对较低且气候相对干燥时， （ii）在过去的19年里，即当海平面上升且盛行更多潮湿条件时，与盐分有关的分层。在此期间，盐度和分层与季风降水动力学直接相关，季风降水动力学主要受日照和大西洋子午翻转翻转环流（AMOC）强度的强迫。在海因里希球场1和年轻的树妖活动期间，即AMOC崩溃时，南亚降水减弱使分层减少，PP增强。在Bølling–Allerød期间，即AMOC恢复之后，南亚的强降水增加了分层并降低了PP。同样，在全新世中期前后记录的降水峰值与促使PP最小化的更强分层一致。