The Oceanic Biological Pump: Rapid carbon transfer to depth at Continental Margins during Winter

Laurenz Thomsen,Jacopo Aguzzi,Andrea Ogston,Corrado Costa,Fabio De Leo,Autun Purser

doi:10.1038/s41598-017-11075-6

Abstract

The oceanic biological pump is responsible for the important transfer of CO2-C as POC “Particulate Organic Carbon” to the deep sea. It plays a decisive role in the Earth’s carbon cycle and significant effort is spent to quantify its strength. In this study we used synchronized daily time-series data of surface chlorophyll-a concentrations from the NASA’s MODIS satellite in combination with hourly to daily observations from sea surface buoys and from an Internet Operated Vehicle (IOV) on the seafloor within Barkley Canyon (Northeast Pacific) to investigate the importance of winter processes in the export of fresh phytodetritus. The results indicate that phytoplankton pulses during winter can be as important in POC transfer to depth as the pulses associated with spring and summer blooms. Short winter phytoplankton pulses were observed to disappear from surface waters after low-pressure systems affected the area. Pulses of chlorophyll reached the IOV, at 870 m depth on the canyon seafloor, 12–72 hours later. These observed short pulses of biological carbon production regularly observed in the region from December to March have not been considered a significant component of the biological pump when compared with the denser summer productivity blooms.

Highlights

The oceanic biological pump is responsible for the important transfer of CO2-C as particulate organic carbon (POC) “Particulate Organic Carbon” to the deep sea
For an annual overview on surface productivity, we followed the seasonal distribution of chlorophyll-a at the sea surface from January 2010 to December 2011 using 8-day composite images provided by the NASA-MODerate resolution Imaging Spectrometer (MODIS) satellite for the continental margin off southwest Vancouver Island[14]
Conceptual model linking winter-driven physical forcing to small phytoplankton blooms and subsequent export to the deep sea at continental margins with canyons

Summary

Introduction

The oceanic biological pump is responsible for the important transfer of CO2-C as POC “Particulate Organic Carbon” to the deep sea. The influence of highly productive continental margins on deep ocean organic carbon inventories is increasingly represented in global carbon models[2], with this biological pump being the core subject of several international multidisciplinary research programs conducted over the last 30 years[3,4,5] Submarine canyons along these margins have been identified as potential rapid conduits for POC to the deep ocean via lateral advection, but detailed long-term observations on how these fluxes may be funneled through canyons are few[6], despite the fact that there are approximately 9,500 canyons in the world’s oceans[7]. We hypothesize that intermittent mixing, and a resulting oscillation in the mixed layer depth, prior to strong seasonal stratification and the spring bloom, result in pulsed export events of POC to depth These have a similar effect on the biological pump when compared to spring/summer conditions. These results indicate that the potential importance of winter surface productivity pulses to deep-sea ecosystems should be reconsidered

Methods

Results

Conclusion