Low-nutrient organic matter in the Sargasso Sea thermocline: A hypothesis for its role, identity, and carbon cycle implications

Fawcett, Sarah E.; Johnson, Kenneth S.; Riser, Stephen C.; Oostende, N. Van; Sigman, Daniel M.

doi:10.1016/j.marchem.2018.10.008

Cited by 37 publications

(64 citation statements)

References 154 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This means that NH 4 + is preferably regenerated, as that has been observed (Stukel et al, ). In addition, a significant portion of the respired POCsusp and DOC in the lower euphotic could be the nutrient‐poor, gel‐like organic matter, which is produced under nutrient‐limited conditions (Fawcett et al, ). Therefore, remineralization of gel‐like organic matter produces much less quantity of nitrate than expected.…”

Section: Discussionmentioning

confidence: 99%

“…Here annual NCP inferred from the temporal evolution of oxygen (O 2 ) and dissolved inorganic carbon at the Bermuda Atlantic Time‐series Study (BATS) site is 3.8 ± 1.2 mol C·m −2 ·year −1 (Emerson, ). In contrast, the downward flux of TOC at 150 m is estimated to be only 23–77% of annual NCP (Carlson et al, ; Emerson, ; Fawcett et al, ; Martin et al, ; Michaels et al, ). The underlying biophysical mechanisms responsible for the disagreement between the annual NCP and TOC flux remain uncertain.…”

Section: Introductionmentioning

confidence: 99%

“…In fact, POCsusp dominates the standing stock of POC in the ocean (Cavan et al, ; Riley et al, ). The contributors to TOC export near BATS are 0.88 ± 0.14 mol C·m −2 ·year −1 at 150 m from POCsink (Lomas et al, ), 0.4–1.4 mol C·m −2 ·year −1 at 100 m from DOC (Carlson et al, ; Hansell & Carlson, ), 0–0.1 mol C·m −2 ·year −1 at 100 m from POCsusp (Omand et al, ), and 0.06 mol C·m −2 ·year −1 from zooplankton migration (Steinberg et al, ; see also Fawcett et al, ). Summing these, the upper bound estimate of TOC export at 100–150 m is 2.4 mol C·m −2 ·year −1 .…”

Section: Introductionmentioning

confidence: 99%

“…A quantitative understanding of the mismatch between NCP and carbon export requires assessment of the uncertainties in both components. Annual NCP at BATS has been estimated from 2 to 5 mol C·m −2 ·year −1 (Fawcett et al, 2018), with the spread attributed to methodology. The lowest NCP estimates (2 ± 1 mol C·m −2 ·year −1 ) come from annual budgets of mixed layer dissolved inorganic carbon (Gruber et al, 1998;Marchal et al, 1996;Ostle et al, 2015) or oxygen (Luz & Barkan, 2009;Munro et al, 2013;Ostle et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Isopycnal Processes Allow for Summertime Heterotrophy Despite Net Oxygen Accumulation in the Lower Euphotic Zone of the Western North Atlantic Subtropical Gyre

Chen

McKinley

2019

Global Biogeochemical Cycles

View full text Add to dashboard Cite

In the oligotrophic subtropical gyre of the North Atlantic, the processes that allow for an imbalance between annual biological productivity and organic carbon export have been sought for decades. We use biogeochemical data from profiling floats and 26‐year bottle samples off Bermuda to provide the first evidence for a mechanism that allows for heterotrophy in the presence of oxygen accumulation in the lower euphotic zone (50–100 m) during the stratified season. After the spring bloom, surface waters that are enriched in oxygen and organic matter, but low in nitrate, are subducted and transported along the seasonal isopycnals that progressively displace downward. Due exclusively to this downward displacement, a positive 50‐ to 100‐m depth‐integrated O2 anomaly appears (1,688 ± 545 mmol O2/m2) from mid‐May to mid‐October. Neglecting this effect of isopycnal displacement would suggest an excess of biological productivity over remineralization at 50–100 m (344 ± 330 mmol O2/m2). Yet, when these changes are differenced, significant along‐isopycnal oxygen consumption (−1,344 ± 537 mmol O2/m2) is identified. After accounting for mixing, net biological‐driven oxygen consumption is still found (−827 ± 509 mmol O2/m2), which indicates heterotrophy. Remineralization of sinking and suspended organic matters at 50–100 m could support 90 ± 67% of the heterotrophic demand. Our analysis also shows that the spread in the biological‐driven oxygen sink is linked to the strength of isopycnal displacement that modulates the supply of nutrients and organic matters. This along‐isopycnal transport and heterotrophy in the lower euphotic zone reduces carbon export at 100 m and helps to resolve previously noted imbalances between surface biological productivity and total organic carbon export.

show abstract

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Isopycnal Processes Allow for Summertime Heterotrophy Despite Net Oxygen Accumulation in the Lower Euphotic Zone of the Western North Atlantic Subtropical Gyre

Chen

McKinley

2019

Global Biogeochemical Cycles

View full text Add to dashboard Cite

show abstract

“…Given the ability of a float array to make observations on seasonal to interannual timescales at basin to global scales, significant effort has been devoted to integrating biogeochemical sensors onto profiling floats, including oxygen [78,79], nitrate [80], and bio-optical measurements for chlorophyll a fluorescence [81] and particle backscatter [82]. These biogeochemical profiling floats have been used to study production dynamics [83][84][85][86][87], nutrient delivery to oligotrophic waters [88], oxygen minimum zone dynamics [89], regional air-sea fluxes [90][91][92], and elemental ratios [93]. A pCO 2 sensor has been integrated onto a profiling float [94], but has not left the prototyping phase due to issues such as long response time, need for frequent recalibration, and high power requirements.…”

Section: Global Ocean Observations From Profiling Floatsmentioning

confidence: 99%

Observing Changes in Ocean Carbonate Chemistry: Our Autonomous Future

Bushinsky

Takeshita

Williams

2019

Curr Clim Change Rep

View full text Add to dashboard Cite

Purpose of Review We summarize recent progress on autonomous observations of ocean carbonate chemistry and the development of a network of sensors capable of observing carbonate processes at multiple temporal and spatial scales. Recent Findings The development of versatile pH sensors suitable for both deployment on autonomous vehicles and in compact, fixed ecosystem observatories has been a major development in the field. The initial large-scale deployment of profiling floats equipped with these new pH sensors in the Southern Ocean has demonstrated the feasibility of a global autonomous open-ocean carbonate observing system. Summary Our developing network of autonomous carbonate observations is currently targeted at surface ocean CO 2 fluxes and compact ecosystem observatories. New integration of developed sensors on gliders and surface vehicles will increase our coastal and regional observational capability. Most autonomous platforms observe a single carbonate parameter, which leaves us reliant on the use of empirical relationships to constrain the rest of the carbonate system. Sensors now in development promise the ability to observe multiple carbonate system parameters from a range of vehicles in the near future.

show abstract

Regionally variable contribution of dissolved organic phosphorus to marine annual net community production

Letscher

Wang

Liang

et al. 2022

Preprint

View full text Add to dashboard Cite

Marine dissolved organic phosphorus (DOP) can serve as an organic nutrient to marine autotrophs, helping to sustain a portion of annual net community production (ANCP). Numerical models of ocean circulation and biogeochemistry have diagnosed the magnitude of this process at regional to global scales but have thus far been validated against DOP observations concentrated within the Atlantic basin. Here we assimilate a new marine DOP dataset with global coverage to optimize an inverse model

show abstract

Low-nutrient organic matter in the Sargasso Sea thermocline: A hypothesis for its role, identity, and carbon cycle implications

Cited by 37 publications

References 154 publications

Isopycnal Processes Allow for Summertime Heterotrophy Despite Net Oxygen Accumulation in the Lower Euphotic Zone of the Western North Atlantic Subtropical Gyre

Isopycnal Processes Allow for Summertime Heterotrophy Despite Net Oxygen Accumulation in the Lower Euphotic Zone of the Western North Atlantic Subtropical Gyre

Observing Changes in Ocean Carbonate Chemistry: Our Autonomous Future

Regionally variable contribution of dissolved organic phosphorus to marine annual net community production

Contact Info

Product

Resources

About