Results express | mid-latitude Pacific northwest region of algal blooms and mixing layer carbon pump in winter
Recently, Xing Xiaogang, Associate researcher of our department and others published a paper "Enhanced Winter Carbon Export Observed by BGC-Argo in the Northwest" in Geophysical Research Letters, an internationally renowned journal Pacific Ocean ". In this study, biogeochemical buoy (BCC-ARGO) data were used to analyze the characteristics of winter algal blooms and carbon pumps in the mid-latitude Northwest Pacific Ocean caused by rapid changes in the mixed layer. The collaborators included Professor Chai Fan and Professor Mark Wells, Associate Researcher Chen Shuangling and postdoctoral researcher Lin Sheng from the University of Maine, USA.
Marine biological pumps continuously absorb atmospheric CO2 into the upper ocean through photosynthesis of phytoplankton, and continue to transport it to the lower ocean in the form of organic carbon, which plays an important regulatory role in maintaining atmospheric CO2 concentration and alleviating global warming. Mixed-layer Pump is an important component of biological Pump. Through the rapid change of Mixed layer, particulate organic carbon is exported in large quantities from the light permeable layer to the low light layer (FIG. 1). Previously, it was generally believed that this process only appeared at the turn of winter and spring, and the output efficiency was high only in the high latitude sea area. In this study, the BGC-ARgo buoy, which was previously placed in the mid-latitude region of the Northwest Pacific by the laboratory, was used to obtain daily high-frequency observation data for nine consecutive months (FIG. 2). It was found that from late January to early March, intermittent winter storms caused rapid changes in the mixed layer over the ocean, and algal blooms occurred when the mixed layer became shallower. When the mixed layer deepens, the rapid output of particles from the surface layer to the deep layer occurs. A single mixed-layer carbon pumping event generally lasted only 5 days, but the total carbon output to the euphotic layer reached 8.927C m-2 in one and a half months, which was twice the annual average carbon output efficiency of the sea area, and even reached 30% of the carbon output efficiency of the North Atlantic spring algal bloom.
Figure 1. Schematic diagram of carbon pump process in mixed layer. T0 and T2 represent the start and end times, and the corresponding mixing layer is shallow (MLD0 and MLD2), while T1 represents the deep mixing event (MLD1). The red curve represents the distribution of particulate organic carbon in the water column. The "carbon pumping phase" (T0 to T1) rapidly transported the surface phytoplankton downward through the deepening of the mixed layer, and supplemented the mixed layer with nutrients. The shallow mixed layer of the "algal bloom phase" (T1 to T2) isolates the previously exported particulate matter (C+D -(A+B)) back to the sea surface, thus completing the rapid export of surface particulate matter. As the mixed layer becomes shallower again and the light in the mixed layer is sufficient, the algal bloom event will also provide new biomass for the next carbon pump in the mixed layer.
Figure 2 Time series of BGC-ARgo buoy locations and observation profiles (December 2018 -- April 2019). (a) Buoy track; (b) temperature; (c) chlorophyll concentration; (d) Particulate organic carbon concentration; (e) Fluorescence soluble organic matter concentration profile. The solid black line represents the depth of the mixing layer, and the dotted white line represents that the buoy was in the center of the "recirculating vortex zone" until March 17.These findings refresh our understanding of mixed-layer carbon pumps, which can be as efficient in mid-latitude seas as in high-latitude seas, occur earlier and more often than expected. 10 days by simulating conventional Argo buoy observation frequency and frequency up to 5 days observation results, found that the low frequency observation significantly underestimated the carbon output efficiency (90% less compared with calculation results of daily data), and may even completely miss out on all the mixed layer rapidly changing events, show that the daily high frequency observation in importance in the study of Marine biological pump. This study not only found that the synoptic-scale mixed-layer carbon pump plays a very important role in the process of ocean carbon output, but also proved that BGC-ARgo buoy has high application value for the observation and research of occasional events (such as typhoon, atmospheric subsidence, etc.).
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PubDate：2020-11-13
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