Decreasing Biological Production and Carbon Export Due to the Barrier Layer: A Case Study in the Bay of Bengal
Decreasing Biological Production and Carbon Export Due to the Barrier Layer: A Case Study in the Bay of Bengal
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DOI：
10.3389/fmars.2021.710051
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发表时间：
2021-09
期刊：
影响因子：
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通讯作者：
Huangchen Zhang;Linbin Zhou;Kaizhi Li;Z. Ke;Yehui Tan
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文献类型：
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作者：
Huangchen Zhang;Linbin Zhou;Kaizhi Li;Z. Ke;Yehui Tan
在近海沃茨和公海中，由淡水引起的阻挡层（BL）是一种常见的物理现象。为了研究BL对生物生产和相关碳输出的影响，在孟加拉湾进行了物理-地球化学调查。由于垂直混合禁止，在BL影响的站点观察到表面磷的严重消耗和营养线的加深。表层叶绿素a（Chl a）的降低和深层Chl a最大值（DCM）的挤压也导致了上述站点Chl a垂直积分值降低约18%。净取样浮游动物的组成发生了变化，与未受影响的站（55.52 ind. m −3）相比，受BL影响的站（29.68 ind. m − 3）的丰度减少了一半。浮游生物录像机（VPR）证实了主要浮游动物群体的这种减少。VPR观测表明，在受BL影响的台站，碎屑丰度较低（低一半），而受BL影响的台站的碳输出通量率估计要低得多（0.31 mg C m−2 d−1），而不是未受影响的台站（0.77 mg C m−2 d−1）。一个理想化的一维营养盐-浮游植物-碎屑模型表明，BL的存在会导致表层营养盐和浮游植物浓度降低，DCM层被挤压，碎屑丰度降低。最后，本研究表明，BL层抑制生物生产和减少碳输出，从而在海洋生态地球化学循环中发挥重要作用。
A freshwater-induced barrier layer (BL) is a common physical phenomenon both in coastal waters and the open ocean. To examine the effects of BL on the biological production and the associated carbon export, a physical-biogeochemical survey was conducted in the Bay of Bengal. Severe depletions of surface phosphorus and the deepening of the nutricline were observed at the BL-affected stations due to the vertical mixing prohibition. The lowered surface chlorophyll a (Chl a) and squeezed deep Chl a maximum (DCM) layer also resulted in the ~18% lowered vertically integrated Chl a at the said stations. The composition of the net-sampled zooplankton was altered, and the abundance decreased by half at the BL-affected station (29.68 ind. m−3) compared with the unaffected station (55.52 ind. m−3). Such reductions in major zooplankton groups were confirmed by a video plankton recorder (VPR). The VPR observation indicated that there was a lower (by one-half) abundance of detritus at the BL-affected station, while the much lower carbon export flux rates were estimated to be at the BL-affected station (0.31 mg C m−2 d−1) rather than the unaffected station (0.77 mg C m−2 d−1). An idealized one-dimensional nutrient-phytoplankton-detritus model identified that the existence of BL can lead to decreased surface nutrients and phytoplankton concentrations, squeezed DCM layers, and lower detritus abundances. Finally, this study indicated that BL layers inhibit biological production and reduce carbon export, thus playing an important role in the ocean biogeochemical cycles.