Primary productivity driven by escalating nutrient fluxes?

初级生产力是由不断增加的养分通量驱动的吗？

• 批准号: NE/R012547/1
• 负责人: Joanne Hopkins
• 金额: $ 12.94万
• 依托单位: NATIONAL OCEANOGRAPHY CENTRE
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2018
• 资助国家: 英国
• 起止时间: 2018 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FR012547%2F1
• 关键词: Primary; productivity; driven; escalating; nutrient

The decline of Arctic Ocean seasonal sea ice cover over the past two decades is a major indicator of polar climate change. Over the same period satellite observations have implied that net primary productivity (NPP) has increased by at least 30%. However, the observed increase in net primary productivity is greater than the predicted response to the declining sea ice, and the consequent lengthening of the ice-free season. This implies that the nitrate-limited Arctic marine ecosystems may also be experiencing increasing nutrient availability. Whilst the impact of riverine nutrients is limited to coastal areas the greatest net primary production increases are observed over the shelf break regions. In these regions the primary source of nutrients is intruding Pacific and Atlantic Water. However this water can reside at depths of 100 or more metres and so physical mixing processes are required to transport nutrients up to the nutrient replete euphotic zone. This leads us to hypothesize that the observed increases in net primary production in the shelf break regions are driven by escalating nutrient fluxes from the deep waters (Atlantic, Pacific) into the euphotic zone as a result of enhanced vertical mixing rates. However, there is a very strong seasonality in the availability of light in the Arctic, due to both the formation of sea ice and also changing day length - from the perpetual darkness of winter to the mid-night sun - enabling accumulation of nutrients close to the surface in winter and so implying a strong seasonal cycle in nutrient fluxes to the surface layer. Furthermore our own turbulence measurements have shown mixing in the Arctic to be highly intermittant (and in consequence fluxes varying by up to 3 orders of magnitude) on timescales as short as an hour. These facts imply that in order to quantify the flux of nutrients from intermediate depths towards the sea surface measurements are required which resolve timescales from hourly to seasonally. The aim of this project is to test the hypothesis that increased primary production is promoted by increased availability of nutrients resulting from increased nutrient fluxes. Data will be collected to test this hypothesis by employing novel acoustic Doppler techniques developed at Bangor University to make turbulent mixing rate and nutrient flux estimates from moorings at contrasting locations around the Arctic shelf break, on timescales from hourly to the full seasonal cycle. These will then be compared to baseline measurements made at these locations by ourselves and others during the recent 2007/8 International Polar Year. The new measurements will be integrated with coincident fluorescence timeseries measurement, within the framework of a biogeochemical model, to quantify the impact of the observed changes in the nutrient environment, on net primary productivity, and to deduce intra-seasonal ecosystem responses to specific flux events.

过去二十年北冰洋季节性海冰覆盖面积的减少是极地气候变化的一个主要指标。同期卫星观测表明，净初级生产力 (NPP) 增加了至少 30%。然而，观测到的净初级生产力的增长大于对海冰减少以及随之而来的无冰季节延长的预测反应。这意味着硝酸盐有限的北极海洋生态系统也可能正在经历营养可用性的增加。虽然河流养分的影响仅限于沿海地区，但在陆架断裂地区观察到最大的净初级生产力增长。在这些地区，营养物质的主要来源是侵入太平洋和大西洋水域。然而，这些水可能存在于 100 米或更深的深度，因此需要物理混合过程将营养物质输送到营养物质丰富的透光区。这使我们推测，所观察到的陆架断裂区域净初级生产力的增加是由于垂直混合率增强而导致从深水（大西洋、太平洋）进入富光带的养分通量不断增加所驱动的。然而，由于海冰的形成和昼长的变化（从冬季的永久黑暗到午夜的阳光），北极的光照有很强的季节性，使得营养物质在接近冬季地表，因此意味着流向表层的养分通量存在强烈的季节性循环。此外，我们自己的湍流测量表明，北极的混合在短至一小时的时间尺度上是高度间歇性的（因此通量变化高达 3 个数量级）。这些事实意味着，为了量化从中等深度到海面的营养物质通量，需要进行测量，以解决从每小时到季节性的时间尺度。该项目的目的是检验以下假设：养分通量增加导致养分可用性增加，从而促进初级生产的增加。将收集数据来检验这一假设，方法是采用班戈大学开发的新型声学多普勒技术，以每小时到整个季节周期的时间尺度，对北极陆架断裂周围对比位置的系泊物进行湍流混合速率和营养通量估计。然后将这些结果与我们和其他人在最近的 2007/8 国际极地年期间在这些地点进行的基线测量进行比较。新的测量将与生物地球化学模型框架内的同步荧光时间序列测量相结合，以量化观察到的营养环境变化对净初级生产力的影响，并推断季节内生态系统对特定通量事件的响应。

项目成果

An Arctic Strait of Two Halves: The Changing Dynamics of Nutrient Uptake and Limitation Across the Fram Strait

北极海峡分为两半：弗拉姆海峡养分吸收和限制的动态变化

• DOI: http://dx.10.1029/2021gb006961
• 发表时间: 2021
• 期刊: Global Biogeochemical Cycles
• 影响因子: 5.2
• 作者: Tuerena R

A warm jet in a cold ocean.

寒冷海洋中的温暖喷气机。

• DOI: http://dx.10.1038/s41467-021-22505-5
• 发表时间: 2021
• 期刊: Nature communications
• 影响因子: 16.6
• 作者: MacKinnon JA