Age determinations of bottom sediments from the Sea of Okhotsk by different methods

On the base of data on benthic foraminifera and sediment biogeochemistry (contents of total organic carbon, calcium carbonate and biogenic opal) in two cores (1265 and 1312 m water depth) from the southeastern Sakhalin slope and one core (839 m water depth) from the southwestern Kamchatka slope variations of the oxygen minimum zone during the last 50 ka in the Okhotsk Sea are reconstructed. The oxygen minimum zone was less pronounced during cooling in the MIS 2 that is suggested to be caused by maximal expansion of the sea ice cover, decrease of marine productivity and increase of production of oxygenated Okhotsk Sea Intermediate Water (OSIW). Two-step-like strengthening of oxygen minimum zone during warmings in the Terminations 1a and 1b was combined with (1) enhanced oxygen consumption due to decomposition of large amount of organic matter in the water column and bottom sediments due to increased marine productivity and supply of terrigenous material from submerged northern shelves; (2) sea ice cover retreat and reduction of OSIW production; (3) freely inflow of the oxygen-depleted intermediate water mass from the North Pacific.

本研究基于萨哈林斜坡东南部两个水深分别为1265米与1312米的岩芯，以及堪察加斜坡西南部一个水深839米的岩芯中的底栖有孔虫数据与沉积物生物地球化学数据（包括总有机碳、碳酸钙及生物成因蛋白石含量），重建了鄂霍次克海过去5万年以来氧最低含氧层（oxygen minimum zone）的演化规律。
在海洋同位素阶段2期（MIS 2）的冷却时段内，氧最低含氧层的发育程度相对较弱；该现象被认为是由海冰覆盖范围达到最大扩张、海洋生产力下降，以及含氧鄂霍次克海中层水（Okhotsk Sea Intermediate Water, OSIW）生成量增加共同引发的。
在终结期1a与1b的升温时段中，氧最低含氧层呈现两步式增强的特征，该过程与以下三种因素共同作用：(1) 海洋生产力提升与北部被淹没陆架输入的陆源物质增多，导致水体与海底沉积物中大量有机质被分解，耗氧量显著升高；(2) 海冰覆盖范围退缩，鄂霍次克海中层水的生成量减少；(3) 北太平洋的贫氧中层水团自由侵入鄂霍次克海。