Carbon and nitrogen productivity during spring in the oligotrophic Indian Ocean along the GO-SHIP IO9N transect
Carbon and nitrogen productivity during spring in the oligotrophic Indian Ocean along the GO-SHIP IO9N transect
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DOI：
10.1016/j.dsr2.2018.11.008
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发表时间：
2019-03-01
影响因子：
3
通讯作者：
Lomas, Michael W.
中科院分区：
文献类型：
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作者：
Baer, Steven E.;Rauschenberg, Sara;Lomas, Michael W.
来自少营养印度洋中部的生物地球化学速率数据有限，但众所周知，物理和化学条件存在地理梯度，可能导致独特的生物地球化学制度。作为GO-SHIP重复水文巡航的参与者，2016年春天在印度洋南纬28度到北纬18度之间，大致沿着东经95度完成了一个样带。通过流式细胞术分析细胞计数样本（浮游植物和异养细菌），并通过稳定同位素示踪剂评估碳和氮生产力孵育的样本，从大约每隔一个纬度的20米处获得。流式细胞术的微生物细胞计数表明，原绿球藻是主要的自养菌，但在赤道附近，聚球菌的贡献越来越大。使用FlowCAM成像的大型真核生物（bbb20 μ m）在近地表水中通常不存在或丰度非常低（< 0.5 μ g C -1）。异养菌占微生物群落生物量的28.4 +/- 4.6%，与自养生物量呈正相关。溶解的硝酸盐和磷酸盐浓度在地表50 m处均低于检测限，而铵在几乎所有站点和深度均未检测到。在50 ~ 200 m深度范围内，硝态氮和磷酸盐浓度由南向北逐渐增加，在北纬6度处最大值分别为31 μ m和2.2 μ m，溶解的NO3-:PO4-常备库的比值始终低于15。尿素浓度（0.02 ~ 0.18 mu mol L-1）呈向北增加的趋势，溶解有机磷浓度（0.25 ~ 0.37 mu mol L-1）在5 ~ 15°S范围内达到最大值，硝态氮、铵态氮和尿素的绝对吸收量在15°S以南均小于1.5 nmol N L-1 h(-1)，硝态氮、铵态氮和尿素的绝对吸收量分别达到3.4、9.0和21 nmol N L-1 h（-1）。在1.5 ~ 6.5°n之间，氨氮和尿素的吸收速率始终是硝酸盐吸收速率的3 ~ 8倍，整个样带的平均f比为0.23。初级生产遵循相同的氮吸收趋势，在1.5-6.5°n范围内，局部最大值为7.4-10.8 nmol C L-1 h（-1）。这些数据代表了全球海洋中一个很大但研究不足的区域，即中央寡营养印度洋生物地球化学省的初级生产、氮吸收和浮游植物多样性的一些首次报道的测量结果。
There is limited biogeochemical rate data from the oligotrophic central Indian Ocean, but it is known that there are geographical gradients in the physical and chemical conditions that may lead to unique biogeochemical regimes. As participants on a GO-SHIP repeat hydrography cruise, a transect was completed in spring of 2016 from 28 degrees S to 18 degrees N in the Indian Ocean, roughly along the 95 degrees E meridion. Cell count samples (phytoplankton and heterotrophic bacteria) analyzed by flow cytometry, and samples for carbon and nitrogen productivity incubations, assessed by stable isotopic tracers, were obtained from 20 m at approximately every other degree of latitude. Microbial cell counts by flow cytometry indicate that Prochlorococcus was the principal autotroph, but with increasing contributions of Synechococcus around the equator. Large eukaryotes (> 20 mu m), imaged using FlowCAM, were generally absent or in very low abundance (< 0.5 mu g C L-1) from near-surface waters. Heterotrophic bacteria contributed 28.4 +/- 4.6% of the microbial community biomass and were positively correlated to autotrophic biomass. Dissolved nitrate and phosphate concentrations were below detection limits throughout the surface 50 m, while ammonium was undetectable at almost all stations and depths. In the 50-200 m depth range, nitrate and phosphate concentrations steadily increased from south to north, reaching a maximum of 31 and 2.2 mu M respectively north of 6 degrees N. The ratio of dissolved NO3-:PO4- standing stocks was always below 15. Urea concentrations (0.02-0.18 mu mol L-1) showed an increasing trend towards the north and dissolved organic phosphorus concentrations (0.25-0.37 mu mol L-1) had a maxima between 5 and 15 degrees S. Absolute uptake rates of nitrate, ammonium and urea were all less than 1.5 nmol N L-1 h(-1) south of 15 degrees S, and increased until local maxima of 3.4, 9.0, and 21 nmol N L-1 h(-1) for nitrate, ammonium, and urea respectively, were reached between 1.5 and 6.5 degrees N. Ammonium and urea uptake rates were consistently 3-8 times higher than nitrate uptake rates, with a mean f-ratio of 0.23 for the entire transect. Primary production followed the same trend of nitrogen uptake, with a local maximum of 7.4-10.8 nmol C L-1 h(-1) found 1.5-6.5 degrees N. These data represent some of the first reported measurements of primary production, nitrogen uptake, and phytoplankton diversity across biogeochemical provinces in the central oligotrophic Indian Ocean a large but understudied region of the global ocean.