Two oceanographic cruises were completed in September 2016 and August 2017 to investigate the distribution of particulate organic matter (POM) across the northeast Chukchi Shelf. Both periods were characterized by highly stratified conditions, with major contrasts in the distribution of regional water masses that impacted POM distributions. Overall, surface waters were characterized by low chlorophyll fluorescence (Chl Fl < 0.8 mg m−3) and particle beam attenuation (
Production of particulate organic carbon (POC) in nutrient-rich coastal waters over continental shelves, its export to depth, and its transport to deeper ocean waters is a poorly quantified component of the global carbon cycle. A critical step in quantifying this vertical transport is identifying shelf processes that export phytoplankton out of the euphotic zone. During cruises of the Santa Barbara Coastal Long Term Ecological Research project, we discovered substantial chlorophyll
- Award ID(s):
- 1831937
- PAR ID:
- 10467588
- Publisher / Repository:
- Inter Research
- Date Published:
- Journal Name:
- Marine Ecology Progress Series
- Volume:
- 719
- ISSN:
- 0171-8630
- Page Range / eLocation ID:
- 41 to 63
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract c p < 0.3 m−1) values, and low concentrations of particulate organic carbon (POC < 8 mmol m−3), chlorophyll and pheophytin (Chl + Pheo < 0.8 mg m−3), and suspended particulate matter (SPM ∼2 g m−3). Elevated Chl Fl and Chl + Pheo (∼2 mg m−3) values measured at mid‐depths below the pycnocline defined the subsurface chlorophyll maxima (SCM), which exhibited moderate POC (∼10 mmol m−3),c p(∼0.4 m−1) and SPM (∼3 g m−3). In contrast, deeper waters below the pycnocline were characterized by low Chl Fl and Chl + Pheo (∼0.7 mg m−3), highc p(>1.5 m−1) and SPM (>8 g m−3) and elevated POC (>10 mmol m−3). POM compositions from surface and SCM regions of the water column were consistent with contributions from active phytoplankton sources whereas samples from bottom waters were characterized by high Pheo/(Chl + Pheo) ratios (>0.4) indicative of altered phytoplankton detritus. Marked contrasts in POM were observed in both surface and middepth waters during both cruises. Increases in chlorophyll and POC consistent with enhanced productivity were measured in middepth waters during the September 2016 cruise following a period of downwelling‐favorable winds, and in surface waters during the August 2017 cruise following a period of upwelling‐favorable winds. -
Dolan, John (Ed.)Abstract During two cruises in the oligotrophic oceanic Gulf of Mexico, we deployed sediment traps at three depths: center of the euphotic zone (EZ) (60 m), base of the EZ (117–151 m), and in the twilight zone (231 m). Organic carbon export declined with depth from 6.4 to 4.6 to 2.4 mmol C m−2 d−1, suggesting that net particle production was concentrated in the upper EZ. Net primary production varied from 24 to 29 mmol C m−2 d−1, slightly more than half in the upper EZ. Export ratios varied from 11 to 25%. Trap measurements of chlorophyll and phaeopigments allowed us to quantify fluxes of fresh phytoplankton and herbivorous fecal pellets, respectively, which were both minor contributors to total flux, although their contributions varied with depth. Phytoplankton flux was more important from the upper to lower EZ; fecal pellets were more important at the EZ base and below. C:N elemental ratios and 13C and 15N isotope analyses indicated particle transformations within and beneath the EZ. 234Th-238U disequilibrium measurements varied, likely reflecting the mixing of water from multiple regions over the ~month-long time-scale of 234Th. Our results highlight the complexity of the biological carbon pump in oligotrophic regions.more » « less
-
more » « less
Abstract In eastern boundary current systems, strong coastal upwelling brings deep, nutrient‐rich waters to the surface ocean, supporting a productive food web. The nitrate load in water masses that supply the region can be impacted by a variety of climate‐related processes that subsequently modulate primary productivity. In this study, two coastal upwelling regimes along central and southern California were sampled seasonally for nitrogen and oxygen stable isotopes of nitrate (i.e., nitrate isotopes) over several years (2010–2016) on 14 California Cooperative Oceanic Fisheries Investigations (CalCOFI) cruises. Seasonal, interannual, and spatial variations in euphotic zone nitrate isotopes were largely driven by the extent of nitrate utilization, sometimes linked to iron limitation of diatom productivity. Pronounced isotopic enrichment developed with the El Niño conditions in late 2015 and early 2016 which likely resulted from increased nitrate utilization linked to reduced nitrate supply to the euphotic zone. Differential enrichment of nitrogen and oxygen isotopes was observed in the surface ocean, suggesting that phytoplankton increased their reliance on locally nitrified (recycled) nitrate during warmer and more stratified periods. Overall, nitrate isotopes effectively differentiated important euphotic zone processes such as nitrate assimilation and nitrification, while archiving the influence of disparate controls such as iron limitation and climatic events through their effects on nitrate utilization and isotopic fractionation.
-
more » « less
Climate change is altering global ocean phenology, the timing of annually occurring biological events. We examined the changing phenology of the phytoplankton accumulation season west of the Antarctic Peninsula to show that blooms are shifting later in the season over time in ice-associated waters. The timing of the start date and peak date of the phytoplankton accumulation season occurred later over time from 1997 to 2022 in the marginal ice zone and over the continental shelf. A divergence was seen between offshore waters and ice-associated waters, with offshore bloom timing becoming earlier, yet marginal ice zone and continental shelf bloom timing shifting later. Higher chlorophyll
a (chla ) concentration in the fall season was seen in recent years, especially over the northern continental shelf. Minimal long-term trends in annual chla occurred, likely due to the combination of later start dates in spring and higher chla in fall. Increasing spring wind speed is the most likely mechanism for later spring start dates, leading to deeper wind mixing in a region experiencing sea ice loss. Later phytoplankton bloom timing over the marginal ice zone and continental shelf will have consequences for surface ocean carbon uptake, food web dynamics, and trophic cascades. -
more » « less
Abstract Herbivorous consumption of primary production is a key transformation in global biogeochemical cycles, directing matter and energy either to higher trophic levels, export production, or remineralization. Grazing by microzooplankton is often poorly constrained, particularly in dynamic coastal systems. Temperate coastal areas are seasonally and spatially variable, which presents both challenges and opportunities to identify patterns and drivers of grazing pressure. Here we report on two winter and one summer week‐long cruises (2018–2019), as part of the new Northeast U.S. Shelf Long‐Term Ecological Research program. During both seasons, coastal waters were colder and fresher, and had higher phytoplankton biomass than waters at the shelf break. The phytoplankton community was dominated by large cells in winter and by small cells in summer. Phytoplankton growth rates ranged from < 0.5 d−1in winter and up to 1.4 d−1in summer and were strongly correlated to temperature, to light availability, and to phytoplankton community size‐structure. Grazing rates were not correlated with total chlorophyll
a , which points to other biological drivers, including species composition in predator‐prey interactions at the first trophic level. The percentage of primary production consumed (%PP) indicated higher trophic transfer in winter (%PP > 50%) than during summer (%PP < 20%), highlighting seasonal shifts in planktonic food web structure and function. These results imply that predictable shifts in environmental conditions can be linked to ecosystem shifts in net primary production. Hierarchies of variability, from localized to interannual and long‐term climate driven, can be understood within the context of sustained measurements of ecosystem properties and function.
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3354/meps14393
