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Silicic acid biogeochemistry in the Gulf of California: Insights from sedimentary Si isotopes

机译：加利福尼亚湾的硅酸生物地球化学：沉积硅同位素的见解

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Iron is considered to play a large role in the cycling of Si in Fe-limited regions of the ocean, but little is known about its role in Si biogeochemistry outside these areas. Here, we present published sediment trap data, new nutrient profiles and high resolution sedimentary records (Si isotopes, Biogenic silica%, N% and C%) from the Gulf of California, a non-Fe-limited region, to investigate the history of Si cycling in this highly productive basin. Modern nutrient profiles show that silicic acid in subsurface waters is in excess relative to nitrate and is therefore incompletely utilized during moderate winter upwelling events. Modern data, however, suggest that during intense upwelling episodes, silicic acid is preferentially utilized relative to nitrate by the biota, which we suggest reflects transient iron limitation. Our new δ ~(30)Si record from the Guaymas Basin shows dramatic variations at millennial timescales. Low δ ~(30)Si values synchronous with Heinrich events are interpreted as resulting from the decline in Si(OH) _4 utilization at times of decreased upwelling strength, while nearly complete Si(OH) _4 utilization was observed at times of invigorated upwelling and increased opal burial during the Holocene, the Blling-Allerd and the last glacial period. We attribute the complete utilization of Si(OH) _4 to the occurrence of transient Fe limitation at these times. Our study highlights the importance of Fe limitation on Si and C cycling in coastal upwelling regions and suggests that upwelling dynamics, in combination with Fe availability, have the potential to modulate marine Si distribution and opal burial even at short timescales.
机译：铁被认为在海洋有限的区域中的硅的循环中起着重要作用，但对于这些区域以外的硅生物地球化学的作用知之甚少。在这里，我们展示了来自非铁限制地区加利福尼亚湾的已公布的沉积物陷阱数据，新的养分概况和高分辨率沉积记录（硅同位素，生物硅％，N％和C％），以调查该地区的历史。斯在这个高产的盆地骑自行车。现代营养素特征表明，地下水中的硅酸相对于硝酸盐而言过量，因此在冬季中等上升事件中未被充分利用。但是，现代数据表明，在剧烈的上升流期间，生物区系相对于硝酸盐优先利用硅酸，我们认为这反映了短暂的铁限制。我们从瓜伊马斯盆地获得的新的δ〜（30）Si记录显示了千禧年尺度上的巨大变化。与Heinrich事件同步发生的低δ〜（30）Si值可解释为上升流强度降低时Si（OH）_4利用率下降的结果，而在上升流增强时Si（OH）_4利用率几乎接近。在全新世，布莱林-阿勒德（Blling-Allerd）和末次冰川时期，蛋白石的埋葬量增加。我们将Si（OH）_4的完全利用归因于这些时间出现的瞬时Fe限制。我们的研究凸显了限制Fe含量对沿海上升流地区Si和C循环的重要性，并暗示上升流动力学结合Fe的利用，即使在很短的时间范围内，也有可能调节海洋Si的分布和蛋白石的埋藏。

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