Biogeochemistry of total organic carbon and nitrogen in the Sargasso Sea: control by convective overturn
Biogeochemistry of total organic carbon and nitrogen in the Sargasso Sea: control by convective overturn
复制标题
DOI：
10.1016/s0967-0645(00)00153-3
复制
发表时间：
2001-01-01
影响因子：
3
通讯作者：
Carlson, CA
中科院分区：
文献类型：
--
作者：
Hansell, DA;Carlson, CA
利用1994-1998年的5年时间序列数据，研究了总有机碳和总有机氮对马尾藻海表层元素循环的贡献。表层总有机碳(TOC)和总有机氮(TON)浓度季节性变化范围分别为60~70um C和4~5.5um N，平均C/N摩尔比为14.4+/-2.2。最高地表浓度在各个夏季期间变化不大，表明TOC的净产生在高度稀缺营养的夏季停止。冬季翻转和水柱的混合既是浓度降低的原因，也是营养物质夹带和随后的新产生之后每年TOC净产生的触发因素。TOC净产生量随冬季混合层深度(MLD)的最大值而变化，混合量越大，TOC净产生量越大。1995年冬季，由于最大混合深度为260米，TOC储量增加了1.4molCm(-2)。在随后的几年中，MLD(<；220m)出现了较浅的峰值，TOC储量增加了<；0.7molCm(-2)。水柱的倾覆有助于将TOC输出到深度(>；100 m)，输出量取决于混合深度(总输出量从0.4到1.4molCm(-2)yr(-1))。出口的总有机碳既包括夏末滞留在表层的物质(常驻总有机碳)，也包括春季开花期新产生的物质(新鲜总有机碳)。居留TOC的输出量在0.5~0.8mol cm-2yr(-1)之间，与冬季最大MLD值变化一致。新鲜TOC的出口范围从零到0.8mol cm-2年(-1)。新鲜TOC只有在冬季MLD达到约200m的门槛值后才能出口。在浅层混合的年份，新鲜TOC出口和表层TOC净产生大大减少。出口TOC的衰减速率也随最大MLD的变化而变化。混合最深的年份导致最高的出口和最高的衰减率(0.003 d(-1))，而较浅和较低的出口导致较低的衰减率(0.0002 d(-1))，这可能是出口材料质量的结果。输出的TOC支持DeltaC：DeltaO的氧气利用，摩尔比从TOC输出低时的0.17到TOC输出高时的0.47不等。我们估计，出口的TOC推动了100-400米深度范围内年氧气利用率的15%-41%。最后，夏季表层TON信号缺乏可变性。缺乏夏季净吨产量的信号表明，该地点的N-2固定作用很小。我们推测，如果N-2的固定是马尾藻海主温跃层N/P比值升高的原因，那么这一过程一定发生在百慕大以南，信号通过墨西哥湾流系统向北传输。(C)2001爱思唯尔科学有限公司。保留所有权利。
The contributions of total organic carbon and nitrogen to elemental cycling in the surface layer of the Sargasso Sea are evaluated using a 5-yr time-series data set (1994-1998). Surface-layer total organic carbon (TOC) and total organic nitrogen (TON) concentrations ranged from 60 to 70 muM C and 4 to 5.5 muM N seasonally, resulting in a mean C:N molar ratio of 14.4 +/- 2.2. The highest surface concentrations varied little during individual summer periods, indicating that net TOC production ceased during the highly oligotrophic summer season. Winter overturn and mixing of the water column were both the cause of concentration reductions and the trigger for net TOC production each year following nutrient entrainment and subsequent new production. The net production of TOC varied with the maximum in the winter mixed-layer depth (MLD), with greater mixing supporting the greatest net production of TOC. In winter 1995, the TOC stock increased by 1.4 mol C m(-2) in response to maximum mixing depths of 260 m. In subsequent years experiencing shallower maxima in MLD ( < 220 m), TOC stocks increased < 0.7 mol C m(-2). Overturn of the water column served to export TOC to depth ( > 100 m), with the amount exported dependent on the depth of mixing (total export ranged from 0.4 to 1.4mol C m(-2) yr(-1)). The exported TOC was comprised both of material resident in the surface layer during late summer (resident TOC) and material newly produced during the spring bloom period ( fresh TOC). Export of resident TOC ranged from 0.5 to 0.8 mol Cm-2 yr(-1), covarying with the maximum winter MLD. Export of fresh TOC varied from nil to 0.8 mol Cm-2 yr(-1) Fresh TOC was exported only after a threshold maximum winter MLD of approximate to 200 m was reached. In years with shallower mixing,fresh TOC export and net TOC production in the surface layer were greatly reduced. The decay rates of the exported TOC also covaried with maximum MLD. The year with deepest mixing resulted in the highest export and the highest decay rate (0.003 d(-1))while shallow and low export resulted in low decay rates (0.0002 d(-1)), likely a consequence of the quality of material exported. The exported TOC supported oxygen utilization at DeltaC:DeltaO, molar ratios ranging from 0.17 when TOC export was low to 0.47 when it was high. We estimate that exported TOC drove 15-41% of the annual oxygen utilization rates in the 100-400m depth range. Finally, there was a lack of variability in the surface-layer TON signal during summer. The lack of a summer signal for net TON production suggests a small role for N-2 fixation at the site. We hypothesize that if N-2 fixation is responsible for elevated N:P ratios in the main thermocline of the Sargasso Sea, then the process must take place south of Bermuda and the signal transported north with the Gulf Stream system. (C) 2001 Elsevier Science Ltd. All rights reserved.