Year: 2022
Type: article
Abstract: Dissolved organic carbon (DOC) produced by primary production in the sunlit ocean can be physically transported to the mesopelagic zone. The majority of DOC exported to this zone is remineralized by heterotrophic microbes over a range of timescales. Capturing a deep convective mixing event is rare, as is observing how microbes respond in situ to the exported DOC. Here, we report ship and Argo float observations from hydrostation North Atlantic Aerosols and Marine Ecosystems Study (NAAMES) 2 Station 4 (N2S4; 47.46°N, 38.72°W), a retentive anticyclonic eddy in the subtropical region of the western North Atlantic. Changes in biogeochemistry and bacterioplankton responses were tracked as the water column mixed to approximately 230 m and restratified over the subsequent 3 days. Over this period, rapid changes in bacterioplankton production (BP) and cell abundance were observed throughout the water column. BP increased by 91% in the euphotic zone (0–100 m) and 55% in the upper mesopelagic zone (100–200 m), corresponding to 33% and 103% increases in cell abundance, respectively. Within the upper mesopelagic, BP upon the occupation of N2S4 (20 ± 4.7 nmol C L–1 d–1) was significantly greater than the average upper mesopelagic BP rate (2.0 ± 1.6 nmol C L–1 h–1) at other stations that had been stratified for longer periods of time. BP continued to increase to 31 ± 3.0 nmol C L–1 d–1 over the 3-day occupation of N2S4. The rapid changes in BP in the upper mesopelagic did not coincide with rapid changes in community composition, but the taxa that increased in their relative contribution included those typically observed in the epipelagic zone. We interpret the subtle but significant community structure dynamics at N2S4 to reflect how injection of labile organic matter into the upper mesopelagic zone by physical mixing supports continued growth of euphotic zone-associated bacterioplankton lineages on a timescale of days.
Language: English
Subfield: Oceanography
Field: Earth and Planetary Sciences
Domain: Physical Sciences
SDG: Life below water
Open Access status: gold
Estimated APC paid: $1,450
Awards: FOOD WEB DYNAMICS PLAY AN IMPORTANT ROLE IN PARTITIONING THE PELAGIC NET COMMUNITY PRODUCTION (NCP) BETWEEN PARTICULATE (POM) AND DISSOLVED ORGANIC MATTER (DOM). APPROXIMATELY 50% OF THE DOM PRODUCED IS RAPIDLY CONSUMED TO MEET BACTERIAL CARBON DEMAND. HOWEVER BIOTIC AND ABIOTIC TRANSFORMATION OF ORGANIC MATTER CAN LEAD TO THE ACCUMULATION OF CARBON-RICH DOM RESISTANT TO RAPID MICROBIAL DEGRADATION IN THE SURFACE OCEAN; A FRACTION OF THIS PERSISTS LONG ENOUGH TO BE ENTRAINED DURING OVERTURN SUCH THAT IT IMPACTS THE EFFICIENCY AND MAGNITUDE OF THE BIOLOGICAL CARBON PUMP. THE VERTICAL REDISTRIBUTION OF DOM RESULTS IN THE GLOBAL OCEAN EXPORT OF ~1.8 PG C FROM THE EUPHOTIC ZONE OR ~20% OF THE TOTAL EXPORT PRODUCTION. THUS VERTICAL EXPORT OF DOM REPRESENTS ONE OF THE FIVE MAJOR FLUX PATHWAYS CENTRAL TO THE EXPORT PROGRAM. THE CONTRIBUTION OF DOM TO EXPORT FLUX IS MOST PRONOUNCED AT HIGH LATITUDES WHERE CONVECTIVE MIXING AND SUBMESOSCALE PROCESSES DELIVER DISSOLVED AND SUSPENDED MATERIALS TO THE DEPTH WHEREBY THE CARBON IS SEQUESTERED FOR DECADES TO MILLENNIA. TO RESOLVE THE CONTRIBUTION DOM TO EXPORT IT IS CRITICAL TO OBTAIN HIGH QUALITY DOM DATA ASSESS THE CONTROLS ON ITS NET PRODUCTION CHEMICALLY CHARACTERIZE THE ACCUMULATED POOL AND QUANTIFY EXPORT; IT IS CRITICAL TO ASSESS THE MICROBIAL BIOAVAILABILITY AT EACH ECOSYSTEM / CARBON CYCLING (ECC) STATE OBSERVED BY THE EXPORTS FIELD CAMPAIGNS IN THE NORTH PACIFIC AND NORTH ATLANTIC. THE GUIDING HYPOTHESES OF THIS PROPOSED PROJECT ARE: H1: GIVEN QUANTIFICATION OF NCP THE NET PRODUCTION (ACCUMULATION) OF DOC IS A PREDICTABLE PROCESS FOR THESE SUBARCTIC SYSTEMS. H2: GIVEN MEASURES OF VERTICAL OVERTURN DOC EXPORT TO THE TWILIGHT ZONE IS A PREDICTABLE PROCESS. THE CARLSON (UCSB) AND HANSELL (RSMAS) TEAM HAS OVER TWO DECADES OF EXPERIENCE RESOLVING TEMPORAL AND BASIN SCALE DISTRIBUTIONS BULK DOC AND DON ACROSS THE GLOBAL OCEAN AND FROM THOSE THEIR CONTRIBUTIONS TO VERTICAL FLUX. THEY HAVE EXPERIENCE DETERMINING THE DIAGENETIC CHARACTERIZATION OF DOM THROUGH THE MEASURE OF SPECIFIC COMPOUNDS SUCH AS THE DISSOLVED COMBINED NEUTRAL SUGAR COMPONENT. THEY HAVE OPTIMIZED THE MICROBIAL REMINERALIZATION BIOASSAYS NECESSARY TO ASSESS THE BIOAVAILABILITY / PERSISTENCE (I.E. EXPORT POTENTIAL) OF THE ACCUMULATED DOM. THE TEAM IS POISED TO GENERATE MISSION-CRITICAL DATA FOR EXPORTS (TABLE 2 OF THE IMPLEMENTATION PLAN) THAT ADDRESS COMPONENTS OF SCIENTIFIC QUESTIONS SQ1 AND SQ2. SPECIFICALLY THIS PROPOSED WORK AIMS TO: A. UNDERSTAND CONTROLS ON THE FRACTIONS OF NET PRIMARY PRODUCTION AND NET COMMUNITY PRODUCTION PARTITIONED AS DOC AND DON B. DETERMINE THE FLUX OF THE MOST LABILE FRACTION OF DOM REQUIRED TO MEET CARBON DEMAND OF HETEROTROPHIC BACTERIAL PRODUCTION (I.E. BACTERIAL CARBON DEMAND) C. DETERMINE DOM BIOAVAILABILITY TO MICROBES AND THE FRACTION OF THE SEASONALLY ACCUMULATED POOL THAT PERSISTS FOR WEEKS TO MONTHS D. ASSESS DOM DIAGENETIC STATE (COMPOSITIONAL VARIATIONS) OVER VARYING ECOSYSTEM / CARBON CYCLING (ECC) STATES. E. EVALUATE PHYSICAL MIXING OF DOM OUT OF THE EUPHOTIC ZONE ITS CONTRIBUTION TO EXPORT AND ITS FATE., G8143621854, G8206856074
OpenAlex ID: W4289535388