Seasonal and long-term dynamics of the upper ocean carbon cycle at Station ALOHA near Hawaii
Seasonal and long-term dynamics of the upper ocean carbon cycle at Station ALOHA near Hawaii
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DOI：
10.1029/2004gb002227
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发表时间：
2004-10-15
影响因子：
5.2
通讯作者：
Gruber, N
中科院分区：
文献类型：
--
作者：
Keeling, CD;Brix, H;Gruber, N
根据溶解无机碳(DIC)、碱度和C-13/C-12比值的14年时间序列(1988-2002年)，在美国JGOFS夏威夷海洋时间序列计划(HOT)的所在地Aloha站调查了上层海洋碳循环的长期趋势和平均季节变化。盐度归一化DIC和计算的海洋PCO(2)分别呈明显的上升趋势，分别为1.2mumol kg(-1)yr(-1)和2.5mumol kg(-1)yr(-1)，而DIc的C-13/C-12同位素比值(以增量(13)C(Oc)表示)以-0.027+/-0.001%yr(-1)的平均速率下降。SDIC和海洋PCO(2)的变化率的一半以上以及C-13/C-12的大部分变化率都归因于从大气中吸收了同位素轻质的人为二氧化碳。剩余趋势似乎主要是由淡水净预算的区域变化引起的，可能与近1997年北太平洋气候系统的体制变化有关。计算的海洋PCO(2)几乎全年都低于大气PCO(2)，导致年平均表层海洋PCO(2)不饱和约18MATM，并导致每年从大气中吸收CO2，我们计算出1.0+/-0.1molm(-2)yr(-1)。我们估计，大约30%的通量与人为二氧化碳的吸收有关，其余的与生物中介的有机碳出口有关。使用Gruber等人的诊断模型的修改版本。[1998]在增量(13)C(Oc)的约束下，我们推断群落有机碳净生产量(NCP)是产生SDIC观测到的季节变化的主要过程。NCP的年积分为2.3+/-0.8molm(-2)yr(-1)，与以前对副热带北太平洋生物产量的估计相当。Aloha站的海-气气体交换和NCP年综合通量分别约为使用类似估算方法计算的百慕大附近上层海洋通量的三分之二[Gruber等人，1998年、2002年]。然而，夏威夷附近的SDIC和Delta(13)C(Oc)的季节幅度仅为百慕大附近的一半，这是因为夏威夷附近的海气交换和NCP倾向于相互对立，而在百慕大附近则相互加强。
Long-term trends and average seasonal variability in the upper ocean carbon cycle are investigated at Station ALOHA, the site of the U. S. JGOFS Hawaii Ocean Time series program ( HOT), on the basis of a 14-year time series (1988-2002) of dissolved inorganic carbon (DIC), alkalinity, and C-13/C-12 ratio of DIC data. Salinity-normalized DIC (sDIC) and computed oceanic pCO(2) show distinct upward trends of 1.2 +/- 0.1 mumol kg(-1) yr(-1) and 2.5 +/- 0.1 muatm yr(-1), respectively, while the C-13/C-12 isotopic ratio of DIC (expressed as delta(13)C(oc)) decreases at a mean rate of -0.027 +/- 0.001% yr(-1). More than half of the rates of change in sDIC and oceanic pCO(2), and most of the change in C-13/C-12, are attributed to the uptake of isotopically light anthropogenic CO2 from the atmosphere. The residual trends appear to be caused mainly by a regional change in the net freshwater budget, perhaps associated with a regime change of the North Pacific climate system near 1997. Computed oceanic pCO(2) is below atmospheric pCO(2) for nearly the entire year, leading to an annual mean surface ocean pCO(2) undersaturation of about 18 matm, and to an annual uptake of CO2 from the atmosphere, which we compute to be 1.0 +/- 0.1 mol m(-2) yr(-1). We estimate that about 30% of this flux relates to the uptake of anthropogenic CO2, and the remainder to biologically mediated export of organic carbon. Using a modified version of the diagnostic model of Gruber et al. [ 1998], constrained by delta(13)C(oc), we infer net community production of organic carbon (NCP) to be the dominant process generating the observed seasonal variability in sDIC. The annual integral of NCP, 2.3 +/- 0.8 mol m(-2) yr(-1), is comparable to previous estimates of biological production in the subtropical North Pacific. Annually integrated fluxes of air-sea gas exchange and NCP at Station ALOHA are each about two thirds of those computed for the upper ocean near Bermuda using similar methods of estimation [ Gruber et al., 1998, 2002]. However, the seasonal amplitudes of sDIC and delta(13)C(oc) near Hawaii are only half as large as near Bermuda, because air-sea gas exchange and NCP tend to oppose each other near Hawaii, but reinforce each other near Bermuda.