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Deep water formation in the North Pacific and deglacial CO_2 rise

机译：北太平洋深水形成和冰期CO_2上升

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Deep water formation in the North Atlantic and Southern Ocean is widely thought to influence deglacial CO_2 rise and climate change; here we suggest that deep water formation in the North Pacific may also play an important role. We present paired radiocarbon and boron isotope data from foraminifera from sediment core MD02-2489 at 3640m in the North East Pacific. These show a pronounced excursion during Heinrich Stadial 1, with benthic-planktic radiocarbon offsets dropping to ~350 years, accompanied by a decrease in benthic δ~(11)B. We suggest that this is driven by the onset of deep convection in the North Pacific, which mixes young shallow waters to depth, old deep waters to the surface, and low-pH water from intermediate depths into the deep ocean. This deep water formation event was likely driven by an increase in surface salinity, due to subdued atmospheric/monsoonal freshwater flux during Heinrich Stadial 1. The ability of North Pacific Deep Water (NPDW) formation to explain the excursions seen in our data is demonstrated in a series of experiments with an intermediate complexity Earth system model. These experiments also show that breakdown of stratification in the North Pacific leads to a rapid ~30 ppm increase in atmospheric CO_2, along with decreases in atmospheric δ~(13)C and Δ~(14)C, consistent with observations of the early deglaciation. Our inference of deep water formation is based mainly on results from a single sediment core, and our boron isotope data are unavoidably sparse in the key HS1 interval, so this hypothesis merits further testing. However, we note that there is independent support for breakdown of stratification in shallower waters during this period, including a minimum in δ~(15)N, younging in intermediate water ~(14)C, and regional warming. We also re-evaluate deglacial changes in North Pacific productivity and carbonate preservation in light of our new data and suggest that the regional pulse of export production observed during the B?lling-Aller?d is promoted by relatively stratified conditions, with increased light availability and a shallow, potent nutricline. Overall, our work highlights the potential of NPDW formation to play a significant and hitherto unrealized role in deglacial climate change and CO_2 rise.
机译：人们广泛认为，北大西洋和南大洋的深水形成会影响冰期CO_2的上升和气候变化。在这里，我们建议北太平洋的深水形成也可能起重要作用。我们提供了东北太平洋3640m沉积物核心MD02-2489的有孔虫的成对放射性碳和硼同位素数据。这些表明在海因里希球场1号期间发生了明显的偏移，底栖-浮游植物的放射性碳偏移下降至〜350年，同时底栖δ〜（11）B减小。我们认为，这是由北太平洋深对流的发生所驱动的，该过程将年轻的浅水混合到深度，将旧的深水混合到地表，以及从中等深度到深海的低pH值水。这种深水形成事件很可能是由于海因里希体育场1期间大气/季风淡水通量减弱而导致地表盐度增加所致。北太平洋深水（NPDW）形成解释我们数据中所见偏移的能力已在2000年得到证明。一系列具有中等复杂度的地球系统模型的实验。这些实验还表明，北太平洋的分层破裂导致大气CO_2迅速增加〜30 ppm，同时大气δ〜（13）C和Δ〜（14）C下降，这与早期冰消的观察结果一致。我们对深水形成的推断主要基于单个沉积物岩心的结果，而且我们的硼同位素数据不可避免地在关键的HS1区间内稀疏，因此该假设值得进一步检验。但是，我们注意到，在此期间，浅层水的分层分解得到了独立的支持，包括δ〜（15）N的最小值，中间水〜（14）C的年轻化以及区域变暖。根据我们的新数据，我们还重新评估了北太平洋生产力和碳酸盐保存的冰河变化，并认为在Blling-Aller？d期间观察到的出口生产的区域脉动是由相对分层的条件所促进的，光的可利用性增加了和浅而有效的营养素。总体而言，我们的工作强调了NPDW形成在冰消气候变化和CO_2上升中发挥迄今尚未发挥的重要作用的潜力。

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