ORCID Profile
0000-0002-8376-0843
Current Organisation
Oregon State University
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Publisher: American Geophysical Union (AGU)
Date: 10-2019
DOI: 10.1029/2019PA003632
Publisher: Proceedings of the National Academy of Sciences
Date: 08-2011
Abstract: Episodic iceberg-discharge events from the Hudson Strait Ice Stream (HSIS) of the Laurentide Ice Sheet, referred to as Heinrich events, are commonly attributed to internal ice-sheet instabilities, but their systematic occurrence at the culmination of a large reduction in the Atlantic meridional overturning circulation (AMOC) indicates a climate control. We report Mg/Ca data on benthic foraminifera from an intermediate-depth site in the northwest Atlantic and results from a climate-model simulation that reveal basin-wide subsurface warming at the same time as large reductions in the AMOC, with temperature increasing by approximately 2 °C over a 1–2 kyr interval prior to a Heinrich event. In simulations with an ocean model coupled to a thermodynamically active ice shelf, the increase in subsurface temperature increases basal melt rate under an ice shelf fronting the HSIS by a factor of approximately 6. By analogy with recent observations in Antarctica, the resulting ice-shelf loss and attendant HSIS acceleration would produce a Heinrich event.
Publisher: American Geophysical Union (AGU)
Date: 08-2017
DOI: 10.1002/2016PA003081
Publisher: American Geophysical Union (AGU)
Date: 06-2017
DOI: 10.1002/2016PA003072
Publisher: Authorea, Inc.
Date: 27-07-2023
DOI: 10.22541/ESSOAR.169049091.16856096/V1
Abstract: Realistic model representation of ocean phytoplankton is important for simulating nutrient cycles and the biological carbon pump, which affects atmospheric carbon dioxide ( p CO) concentrations and, thus, climate. Until recently, most models assumed constant ratios (or stoichiometry) of phosphorous (P), nitrogen (N), silicon (Si), and carbon (C) in phytoplankton, despite observations indicating systematic variations. Here, we investigate the effects of variable stoichiometry on simulated nutrient distributions, plankton community compositions, and the C cycle in the preindustrial (PI) and glacial oceans. Using a biogeochemical model, a linearly increasing P:N relation to increasing PO is implemented for ordinary phytoplankton (P), and a nonlinearly decreasing Si:N relation to increasing Fe is applied to diatoms (P). C:N remains fixed. Variable P:N affects modeled community composition through enhanced PO availability, which increases N-fixers in the oligotrophic ocean, consistent with previous research. This increases the NO fertilization of P, the NO inventory, and the total plankton biomass. Surface nutrients are not significantly altered. Conversely, variable Si:N shifts south the Southern Ocean’s meridional surface silicate gradient, which aligns better with observations, but depresses P growth globally. In Last Glacial Maximum simulations, P respond to more oligotrophic conditions by increasing their C:P. This strengthens the biologically mediated C storage such that dissolved organic (inorganic) C inventories increase by 34-40 (38-50) Pg C and 0.7-1.2 Pg yr more particulate C is exported into the interior ocean. Thus, an additional 13-14 ppm of p CO difference from PI levels results, improving model agreement with glacial observations.
Publisher: Informa UK Limited
Date: 27-05-2015
Publisher: Copernicus GmbH
Date: 14-03-2014
Abstract: Abstract. Marine calcifiers as a plankton functional type (PFT) are a crucial part of the global carbon cycle, being responsible for much of the carbon export to the deep ocean entering via biological pathways. Deep ocean carbon export through calcifiers is controlled by physiological, ecological and biogeochemical factors. This paper describes the implementation of a phytoplankton coccolithophore PFT in the University of Victoria Earth System Climate Model (UVic ESCM), and improvements to the representation of zooplankton calcification and carbon export therein. The described modifications improve model performance with respect to carbon and nutrient fluxes. Primary production, export production, particulate organic carbon and calcite fluxes all fall within independent estimates.
Publisher: American Geophysical Union (AGU)
Date: 07-2019
DOI: 10.1029/2018PA003537
Publisher: American Geophysical Union (AGU)
Date: 13-12-2016
DOI: 10.1002/2016GL070457
Publisher: American Association for the Advancement of Science (AAAS)
Date: 06-11-2020
Abstract: Walczak et al. report that increases in Pacific Ocean ventilation and periods of rapid production of icebergs from the Cordilleran Ice Sheet during the last glacial period preceded episodic iceberg discharges into the Atlantic Ocean (see the Perspective by Jaeger and Shevenell). Marine sediments from the Gulf of Alaska show that increases in vertical mixing of the ocean there correspond with intense iceberg calving from the ice sheet that covered much of high-latitude western North America and that these changes occurred before the analogous Heinrich events in the North Atlantic. Thus, these Pacific climate system reorganizations may have been an early part of a cascade of dynamic climate events with global repercussions. Science , this issue p. 716 see also p. 662
No related grants have been discovered for Andreas Schmittner.