The annual silica cycle of the North Pacific subtropical gyre
The annual silica cycle of the North Pacific subtropical gyre
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DOI：
10.1016/j.dsr.2011.08.001
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发表时间：
2011-10-01
影响因子：
2.4
通讯作者：
Updyke, Brett
中科院分区：
文献类型：
--
作者：
Brzezinski, Mark A.;Krause, Jeffrey W.;Updyke, Brett
在夏威夷海洋时间序列（HOT）观测站ALOHA，对北太平洋副热带环流上部175 m的二氧化硅循环进行了为期两年（2008年1月至2009年12月）的研究。表面沃茨中的硅酸浓度范围为0.6至1.6 μ M，没有明显的季节性趋势。在2008年和2009年，在上层50米的分层达到157 nmol Si L（-1）和81 nmol Si L（-1）d（-1）的值后，每年夏天生物二氧化硅浓度和二氧化硅生产率增加一个数量级。海面高度异常，在150-175米的等温表面的变化分析表明，夏季期间的升高生物硅与反气旋中尺度特征在这两年。在已知的最大大气粉尘浓度期间，春季的成岩二氧化硅浓度增加，在上部10 m处的最大值为36 nmol Si L（-1）。粉尘沉降将提高溶解铁在表面沃茨的水平，但没有硅藻生物量或二氧化硅生产的增加，在近地表海洋成岩二氧化硅浓度表明铁充足的硅藻二氧化硅生产率。低环境中的草酸浓度限制二氧化硅生产率的平均43%的最大潜在率。硅充足只发生在夏季期间，硅藻生物量升高，这表明水华硅藻适应利用低浓度的柠檬酸。HOT的二氧化硅年产量估计为63 mmol Si m（-2）a（-1），夏季水华占全年总量的29%。硅藻估计占浮游植物初级生产力的3-7%，但有机碳输出的9-20%证实了过去的建议，即硅藻对初级生产力和自养生物量的贡献相对较小，但在贫营养的公海生态系统中，二氧化硅是新产品和出口产品的重要贡献者。HOT的二氧化硅年产量比百慕大大西洋时间的估计值低近4倍-从20世纪90年代开始，在马尾藻海的BATS系列研究（BATS）现场，但在真光层底部的年度二氧化硅出口在两个环流之间是相似的，这表明二氧化硅生产及其在表面沃茨中的损失之间的平衡非常不同。相对而言。就二氧化硅而言，BATS是一种更具生产力的系统，其中生物二氧化硅在地表水中高效回收：相比之下，NPSG就二氧化硅而言是一种生产力较低的系统，但较低的回收效率导致新二氧化硅产量的比例要高得多。沃茨。这两个环流显示对比的硅藻生物量的长期趋势，生物硅浓度在HOT自1997年以来一直在增加，但他们一直在减少在BATS建议非常不同的强迫的十年趋势的硅藻在这些环流之间的碳循环的贡献。结合两个环流的数据表明，全球亚热带环流产生13 Tmol Si a（-1），仅为先前估计的51%，将亚热带环流的贡献降低到全球海洋二氧化硅年产量的5-7%。(C)2011爱思唯尔有限公司版权所有。
Silica cycling in the upper 175 m of the North Pacific Subtropical Gyre was examined over a two year period (January 2008-December 2009) at the Hawaii Ocean Time-series (HOT) station ALOHA. Silicic acid concentrations in surface waters ranged from 0.6 to 1.6 mu M, exhibiting no clear seasonal trends. Biogenic silica concentrations and silica production rates increased by an order of magnitude each summer following stratification of the upper 50 m reaching values of 157 nmol Si L(-1) and 81 nmol Si L(-1) d(-1), in 2008 and 2009, respectively. Sea surface height anomalies together with analyses of variability in isothermal surfaces at 150-175 m indicated that the summer periods of elevated biogenic silica were associated with anticyclonic mesoscale features during both years. Lithogenic silica concentrations increased in the spring during the known period of maximum atmospheric dust concentrations with maximum values of 36 nmol Si L(-1) in the upper 10 m. Dust deposition would enhance levels of dissolved iron in surface waters, but there was no response of diatom biomass or silica production to increases in near-surface ocean lithogenic silica concentrations suggesting iron sufficiency of diatom silica production rates.Low ambient silicic acid concentrations restricted silica production rates to an average of 43% of maximum potential rates. Si sufficiency only occurred during the summer period when diatom biomass was elevated suggesting that bloom diatoms are adapted to exploit low silicic acid concentrations. Annual silica production at HOT is estimated to be 63 mmol Si m(-2) a(-1) with summer blooms contributing 29% of the annual total. Diatoms are estimated to account for 3-7% of total phytoplankton primary productivity, but 9-20% of organic carbon export confirming past suggestions that diatoms are relatively minor contributors to primary productivity and autotrophic biomass, but important contributors to new and export production in oligotrophic open-ocean ecosystems.Annual silica production at HOT is nearly 4-fold lower than estimates at the Bermuda Atlantic Time-series Study (BATS) site in the Sargasso Sea from the 1990s, but annual silica export at the base of the euphotic zone is similar between the two gyres indicating very different balances between silica production and its loss in surface waters. On a relative basis. BATS is a more productive system with respect to silica, where biogenic silica is recycled with high efficiency in surface waters: in contrast the NPSG is a lower productivity system with respect to silica, but where lower recycling efficiency leads to a much higher fraction of new silica production. The two gyres show contrasting long-term trends in diatom biomass as biogenic silica concentrations at HOT have been increasing since 1997, but they have been decreasing at BATS suggesting very different forcing of decadal trends in the contribution of diatoms in carbon cycling between these gyres. Combining the data from both gyres indicates that globally subtropical gyres produce 13 Tmol Si a(-1), which is only 51% of previous estimates reducing the contribution of subtropical gyres to 5-7% of global annual marine silica production. (C) 2011 Elsevier Ltd. All rights reserved.