Temporally-resolved mechanisms of deep-ocean particle flux and impact on the seafloor carbon cycle in the northeast Pacific

Abstract. We present a compilation of 127 time series δ13C records from Cibicides wuellerstorfi spanning the last deglaciation (20–6 ka) which is well-suited for reconstructing large-scale carbon cycle changes, especially for comparison with isotope-enabled carbon cycle models. The age models for the δ13C records are derived from regional planktic radiocarbon compilations (Stern and Lisiecki, 2014). The δ13C records were stacked in nine different regions and then combined using volume-weighted averages to create intermediate, deep, and global δ13C stacks. These benthic δ13C stacks are used to reconstruct changes in the size of the terrestrial biosphere and deep ocean carbon storage. The timing of change in global mean δ13C is interpreted to indicate terrestrial biosphere expansion from 19–6 ka. The δ13C gradient between the intermediate and deep ocean, which we interpret as a proxy for deep ocean carbon storage, matches the pattern of atmospheric CO2 change observed in ice core records. The presence of signals associated with the terrestrial biosphere and atmospheric CO2 indicates that the compiled δ13C records have sufficient spatial coverage and time resolution to accurately reconstruct large-scale carbon cycle changes during the glacial termination.

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Deep-Ocean Bottom Pressure Measurements in the Northeast Pacific

Journal of Atmospheric and Oceanic Technology ◽

10.1175/1520-0426(1991)008<0221:dobpmi>2.0.co;2 ◽

1991 ◽

Vol 8 (2) ◽

pp. 221-233 ◽

Cited By ~ 42

Author(s):

M. C. Eble ◽

F. I. Gonzalez

Keyword(s):

Deep Ocean ◽

Ocean Bottom ◽

Pressure Measurements ◽

Bottom Pressure ◽

Ocean Bottom Pressure ◽

Northeast Pacific

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Using new observations and Machine Learning to improve organic sinking processes in the PlankTOM global ocean biogeochemical model

10.5194/egusphere-egu21-11356 ◽

2021 ◽

Author(s):

Anna Denvil-Sommer ◽

Corinne Le Quéré ◽

Erik Buitenhuis ◽

Lionel Guidi ◽

Jean-Olivier Irisson

Keyword(s):

Organic Carbon ◽

Carbon Cycle ◽

Deep Ocean ◽

Ecosystem Dynamics ◽

Global Ocean ◽

Biogeochemical Model ◽

Carbon Export ◽

Mixing Depth ◽

Chl A ◽

Biogeochemical Models

A lot of effort has been put in the representation of surface ecosystem processes in global carbon cycle models, in particular through the grouping of organisms into Plankton Functional Types (PFTs) which have specific influences on the carbon cycle. In contrast, the transfer of ecosystem dynamics into carbon export to the deep ocean has received much less attention, so that changes in the representation of the PFTs do not necessarily translate into changes in sinking of particulate matter. Models constrain the air-sea CO2 flux by drawing down carbon into the ocean interior. This export flux is five times as large as the CO2 emitted to the atmosphere by human activities. When carbon is transported from the surface to intermediate and deep ocean, more CO2 can be absorbed at the surface. Therefore, even small variability in sinking organic carbon fluxes can have a large impact on air-sea CO2 fluxes, and on the amount of CO2 emissions that remain in the atmosphere.In this work we focus on the representation of organic matter sinking in global biogeochemical models, using the PlankTOM model in its latest version representing 12 PFTs. We develop and test a methodology that will enable the systematic use of new observations to constrain sinking processes in the model. The approach is based on a Neural Network (NN) and is applied to the PlankTOM model output to test its ability to reconstruction small and large particulate organic carbon with a limited number of observations. We test the information content of geographical variables (location, depth, time of year), physical conditions (temperature, mixing depth, nutrients), and ecosystem information (CHL a, PFTs). These predictors are used in the NN to test their influence on the model-generation of organic particles and the robustness of the results. We show preliminary results using the NN approach with real plankton and particle size distribution observations from the Underwater Vision Profiler (UVP) and plankton diversity data from Tara Oceans expeditions and discuss limitations.

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Insights into the ocean’s biological carbon pump: What makes marine snow falling into the deep ocean?

10.5194/egusphere-egu21-2143 ◽

2021 ◽

Author(s):

Frederic Le Moigne

Keyword(s):

Carbon Cycle ◽

Global Analysis ◽

Deep Ocean ◽

Ecosystem Structure ◽

Faecal Pellets ◽

Surface Ocean ◽

Mesopelagic Zone ◽

Carbon Pump ◽

Biological Carbon Pump

The oceanic biological carbon pump (BCP) regulates the Earth carbon cycle by transporting part of the photosynthetically fixed CO2 into the deep ocean. Suppressing this mechanism would result in an important increase of atmospheric CO2 level. The BCP occurs mainly in the form of organic carbon particles (POC) sinking out the surface ocean. Various types of particles are produced in surface ocean. They all differ in production, sinking and decomposition rates, vertically and horizontally. The amount of POC transported to depths via these various export pathways as well as their decomposition pathways all have different ecological origins and therefore may response differently to climate change. Here I will briefly review some of the processes driving both particle export out of the euphotic zone (0-100m) as well as particles transport within the mesopelagic zone (100-1000m). In the early 2000s, strong correlations between POC and mineral (calcite an opal) fluxes observed in the deep ocean have inspired the inclusion of &#8220;ballast effect&#8221; parameterizations in carbon cycle models. These relationships were first considered as being universal. However global analysis of POC and mineral ballast fluxes showed that mineral ballasting is important in regions like the high-latitude North Atlantic but that in most places (some of which efficiently exporting) the unballasted fraction often dominates the export flux. In such regions, we later showed that zooplankton-mediated export (presence of faecal pellets) and surface microbial abundance were important drivers of the efficiency of particles export. Similar trends were found globally by including bacteria and zooplankton abundances to a global reanalysis of the global variations of the POC export efficiency. This implies that the whole ecosystem structure from bacteria to fishes, rather than just the phytoplankton community, is important in setting the strength of the biological carbon pump. Further down in the water column (mesopelagic zone), processes impacting the transport of particles are less clear. Sinking particles experience a number of biotic and abiotic transformations during their descent. These includes solubilization, remineralisation, fragmentation, ingestion/active transport, breakdown among others. While some potential factors such as O2 concentration and temperature have been proposed as powerful controls, global evidences are often inconsistent. In the award talk, I will review current challenges related to the role of particles consumption by zooplankton and fishes as well as the role of particles attached prokaryotes (bacteria and archaea) in setting the efficiency of the carbon transport in the mesopelagic zone.

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Deep ocean communities impacted by changing climate over 24 y in the abyssal northeast Pacific Ocean

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1315447110 ◽

2013 ◽

Vol 110 (49) ◽

pp. 19838-19841 ◽

Cited By ~ 69

Author(s):

K. L. Smith ◽

H. A. Ruhl ◽

M. Kahru ◽

C. L. Huffard ◽

A. D. Sherman

Keyword(s):

Pacific Ocean ◽

Deep Ocean ◽

Northeast Pacific ◽

Changing Climate ◽

Northeast Pacific Ocean

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Timing and magnitude of Southern Ocean sea ice/carbon cycle feedbacks

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1908670117 ◽

2020 ◽

Vol 117 (9) ◽

pp. 4498-4504 ◽

Cited By ~ 4

Author(s):

Karl Stein ◽

Axel Timmermann ◽

Eun Young Kwon ◽

Tobias Friedrich

Keyword(s):

Carbon Cycle ◽

Southern Ocean ◽

Sea Ice ◽

General Circulation ◽

Deep Ocean ◽

General Circulation Models ◽

Ice Dynamics ◽

Carbon Cycle Model ◽

Ocean Stratification ◽

Ocean Ventilation

The Southern Ocean (SO) played a prominent role in the exchange of carbon between ocean and atmosphere on glacial timescales through its regulation of deep ocean ventilation. Previous studies indicated that SO sea ice could dynamically link several processes of carbon sequestration, but these studies relied on models with simplified ocean and sea ice dynamics or snapshot simulations with general circulation models. Here, we use a transient run of an intermediate complexity climate model, covering the past eight glacial cycles, to investigate the orbital-scale dynamics of deep ocean ventilation changes due to SO sea ice. Cold climates increase sea ice cover, sea ice export, and Antarctic Bottom Water formation, which are accompanied by increased SO upwelling, stronger poleward export of Circumpolar Deep Water, and a reduction of the atmospheric exposure time of surface waters by a factor of 10. Moreover, increased brine formation around Antarctica enhances deep ocean stratification, which could act to decrease vertical mixing by a factor of four compared with the current climate. Sensitivity tests with a steady-state carbon cycle model indicate that the two mechanisms combined can reduce atmospheric carbon by 40 ppm, with ocean stratification acting early within a glacial cycle to amplify the carbon cycle response.

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Reduced carbon cycle resilience across the Palaeocene–Eocene Thermal Maximum

Climate of the Past ◽

10.5194/cp-14-1515-2018 ◽

2018 ◽

Vol 14 (10) ◽

pp. 1515-1527 ◽

Cited By ~ 2

Author(s):

David I. Armstrong McKay ◽

Timothy M. Lenton

Keyword(s):

Organic Carbon ◽

Carbon Cycle ◽

Deep Ocean ◽

Tipping Point ◽

Tipping Points ◽

Carbon Burial ◽

Thermal Maximum ◽

Organic Carbon Burial ◽

Carbon Release ◽

Hyperthermal Events

Abstract. Several past episodes of rapid carbon cycle and climate change are hypothesised to be the result of the Earth system reaching a tipping point beyond which an abrupt transition to a new state occurs. At the Palaeocene–Eocene Thermal Maximum (PETM) at ∼56 Ma and at subsequent hyperthermal events, hypothesised tipping points involve the abrupt transfer of carbon from surface reservoirs to the atmosphere. Theory suggests that tipping points in complex dynamical systems should be preceded by critical slowing down of their dynamics, including increasing temporal autocorrelation and variability. However, reliably detecting these indicators in palaeorecords is challenging, with issues of data quality, false positives, and parameter selection potentially affecting reliability. Here we show that in a sufficiently long, high-resolution palaeorecord there is consistent evidence of destabilisation of the carbon cycle in the ∼1.5 Myr prior to the PETM, elevated carbon cycle and climate instability following both the PETM and Eocene Thermal Maximum 2 (ETM2), and different drivers of carbon cycle dynamics preceding the PETM and ETM2 events. Our results indicate a loss of “resilience” (weakened stabilising negative feedbacks and greater sensitivity to small shocks) in the carbon cycle before the PETM and in the carbon–climate system following it. This pre-PETM carbon cycle destabilisation may reflect gradual forcing by the contemporaneous North Atlantic Volcanic Province eruptions, with volcanism-driven warming potentially weakening the organic carbon burial feedback. Our results are consistent with but cannot prove the existence of a tipping point for abrupt carbon release, e.g. from methane hydrate or terrestrial organic carbon reservoirs, whereas we find no support for a tipping point in deep ocean temperature.

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