Regulation of a surface chlorophyll hotspot by wind-driven upwelling and eddy circulation in the Santa Barbara Channel, Southern California
Regulation of a surface chlorophyll hotspot by wind-driven upwelling and eddy circulation in the Santa Barbara Channel, Southern California
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DOI：
10.1016/j.pocean.2023.103096
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发表时间：
2023-07
影响因子：
4.1
通讯作者：
R. D. Simons;D. Catlett
中科院分区：
文献类型：
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作者：
R. D. Simons;D. Catlett
虽然美国太平洋沿岸的大部分地区在春季主要是由强烈的风驱动的上升流和浮游植物初级生产的定期季节性周期，但南加州湾由于其不规则的庇护海岸线，具有弱间歇性的风驱动的上升流和低浮游植物浓度。然而，位于加州湾北方南部的圣巴巴拉海峡（SBC）含有浮游植物生物量的异常热点。我们使用3D海洋环流和粒子跟踪模型，经验的温度-硝酸盐关系，卫星观测表面叶绿素从1998年至2007年，以确定如何风驱动的上升流和气旋涡流环流治理浮游植物的SBC动态。我们的研究结果表明，在春季升高的表面叶绿素是由风驱动的上升流和气旋涡流环流的耦合驱动的，并需要风驱动的上升流和涡流环流的停留时间延长的高硝酸盐的存在。长的停留时间，持续的气旋涡流环流，允许硝酸盐运输到表层的风驱动的上升流被保留在SBC足够长的时间，以满足浮游植物营养吸收和积累所需的时间尺度，克服了典型的弱风驱动的上升流的南加州湾。典型的春季上升流期（SUPs）具有高水平的表面叶绿素，这是由上升流强度和气旋性涡旋环流的平衡耦合产生的。在我们1998年和1999年的两年研究中，叶绿素含量与地表叶绿素含量的升高没有关联。与强烈的厄尔尼诺现象相对应的是，1998年的厄尔尼诺现象有着异常微弱的风驱动的上升流，这并没有产生足够的硝酸盐来刺激表面叶绿素的升高。1999年夏季，一次强烈的拉尼娜事件产生了异常强烈的风驱动的上升流，导致硝酸盐含量非常高，但抑制了涡流环流和停留时间，使浮游植物生物量无法在SBC中积累。这些异常的SUPs表明，当风驱动的上升流太强或太弱时，风驱动的上升流和气旋性涡旋环流之间的平衡被破坏，导致表面叶绿素的急剧减少，这可能会变得更加频繁的气候驱动的上升流的变化在未来。
While most of the U.S. Pacific coast is dominated by strong wind-driven upwelling in the spring and regular seasonal cycles of phytoplankton primary production, the Southern California Bight has weak intermittent wind-driven upwelling and low phytoplankton concentrations due to its irregular sheltered coastline. However, the Santa Barbara Channel (SBC), located in the northern Southern California Bight, contains an anomalous hotspot of phytoplankton biomass. We use 3D ocean circulation and particle tracking models, an empirical temperature-nitrate relationship, and satellite observations of surface chlorophyll from 1998 to 2007 to determine how wind-driven upwelling and cyclonic eddy circulation govern phytoplankton dynamics in the SBC. Our findings show that elevated surface chlorophyll in the spring is driven by the coupling of wind-driven upwelling and cyclonic eddy circulation and requires the presence of both high nitrate from wind-driven upwelling and prolonged residence times from eddy circulation. Long residence times, created by persistent cyclonic eddy circulation, allow nitrate transported into the surface layer by wind-driven upwelling to be retained in the SBC long enough to meet the required timescales for phytoplankton nutrient uptake and accumulation, overcoming the typically weak wind-driven upwelling of the Southern California Bight. Typical spring upwelling periods (SUPs) have high levels of surface chlorophyll, which are produced by the balanced coupling of upwelling strength and cyclonic eddy circulation. For two years of our study, 1998 and 1999, the SUP did not correlate with elevated surface chlorophyll. Corresponding to a strong El Niño event, the 1998 SUP had exceptionally weak wind-driven upwelling, which did not produce sufficient levels of nitrate to stimulate elevated surface chlorophyll. For the 1999 SUP, a strong La Niña event produced unusually strong wind-driven upwelling, which resulted in very high levels of nitrate, but suppressed eddy circulation and residence times to the point where phytoplankton biomass could not accumulate in the SBC. These anomalous SUPs illustrate that when wind-driven upwelling is too strong or too weak, the balance between wind-driven upwelling and cyclonic eddy circulation is disrupted, resulting in a dramatic reduction of surface chlorophyll, which may become more frequent with climate-driven upwelling changes in the future.