ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    facet.materialart.
    Unknown
    Effects of parameter indeterminacy in pelagic biogeochemical modules of Earth System Models on projections into a warming future: The scale of the problem (2017)
    AGU (American Geophysical Union) | Wiley
    In:  Global Biogeochemical Cycles, 31 (7). pp. 1155-1172.
    Details
    Publication Date: 2020-02-06
    Description: Numerical Earth System Models are generic tools used to extrapolate present climate conditions into a warming future and to explore geoengineering options. Most of the current-generation models feature a simple pelagic biogeochemical model component that is embedded into a three-dimensional ocean general circulation model. The dynamics of these biogeochemical model components is essentially controlled by so-called model parameters most of which are poorly known. Here we explore the feasibility to estimate these parameters in a full-fledged three-dimensional Earth System Model by minimizing the misfit to noisy observations. The focus is on parameter identifiability. Based on earlier studies, we illustrate problems in determining a unique estimate of those parameters that prescribe the limiting effect of nutrient- and light-depleted conditions on carbon assimilation by autotrophic phytoplankton. Our results showcase that for typical models and evaluation metrics no meaningful “best” unique parameter set exists. We find very different parameter sets which are, on the one hand, equally consistent with our (synthetic) historical observations while, on the other hand, they propose strikingly differing projections into a warming climate.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER (OCEANREP)
  • 2
    facet.materialart.
    Unknown
    A new perspective on environmental controls of marine nitrogen fixation (2015)
    AGU (American Geophysical Union) | Wiley
    In:  Geophysical Research Letters, 42 (11). pp. 4482-4489.
    Details
    Publication Date: 2020-06-29
    Description: Growing slowly, marine N2 fixers are generally expected to be competitive only where nitrogen (N) supply is low relative to that of phosphorus (P) with respect to the cellular N:P ratio (R) of non-fixing phytoplankton. This is at odds with observed high N2 fixation rates in the oligotrophic North Atlantic where the ratio of nutrients supplied to the surface is elevated in N relative to the average R (16:1). In this study, we investigate several mechanisms to solve this puzzle: iron limitation, phosphorus enhancement by preferential remineralization or stoichiometric diversity of phytoplankton, and dissolved organic phosphorus (DOP) utilization. Combining resource competition theory and a global coupled ecosystem-circulation model we find that the additional N and energy investments required for exo-enzymatic break-down of DOP gives N2 fixers a competitive advantage in oligotrophic P-starved regions. Accounting for this mechanism expands the ecological niche of N2-fixers also to regions where the nutrient supply is high in N relative to R, yielding, in our model, a pattern consistent with the observed high N2-fixation rates in the oligotrophic North Atlantic.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER (OCEANREP)
  • 3
    facet.materialart.
    Unknown
    Influence of sea level rise on the dynamics of salt inflows in the Baltic Sea (2015)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Oceans, 120 (10). pp. 6653-6668.
    Details
    Publication Date: 2018-04-27
    Description: The Baltic Sea is a marginal sea, located in a highly industrialized region in Central Northern Europe. Saltwater inflows from the North Sea and associated ventilation of the deep exert crucial control on the entire Baltic Sea ecosystem. This study explores the impact of anticipated sea level changes on the dynamics of those inflows. We use a numerical oceanic general circulation model covering both the Baltic and the North Sea. The model successfully retraces the essential ventilation dynamics throughout the period 1961–2007. A suite of idealized experiments suggests that rising sea level is associated with intensified ventilation as saltwater inflows become stronger, longer, and more frequent. Expressed quantitatively as a salinity increase in the deep central Baltic Sea, we find that a sea level rise of 1 m triggers a saltening of more than 1 PSU. This substantial increase in ventilation is the consequence of the increasing cross section in the Danish Straits amplified by a reduction of vertical mixing
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER (OCEANREP)
  • 4
    facet.materialart.
    Unknown
    Simulated effects of southern hemispheric wind changes on the Pacific oxygen minimum zone (2016)
    AGU (American Geophysical Union) | Wiley
    In:  Geophysical Research Letters, 43 (2). pp. 728-734.
    Details
    Publication Date: 2019-09-23
    Description: A coupled ocean biogeochemistry-circulation model is used to investigate the impact of observed past and anticipated future wind changes in the southern hemisphere on the oxygen minimum zone in the tropical Pacific. We consider the industrial period until the end of the 21st century and distinguish effects due to a strengthening of the westerlies from effects of a southward shift of the westerlies that is accompanied by a poleward expansion of the tropical trade winds. Our model results show that a strengthening of the westerlies counteracts part of the warming-induced decline in the global marine oxygen inventory. A poleward shift of the trade-westerlies boundary, however, triggers a significant decrease of oxygen in the tropical oxygen minimum zone. In a business-as-usual CO2 emission scenario, the poleward shift of the trade-westerlies boundary and warming-induced increase in stratification contribute equally to the expansion of suboxic waters in the tropical Pacific.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER (OCEANREP)
  • 5
    facet.materialart.
    Unknown
    Revisiting "nutrient trapping" in global coupled biogeochemical ocean circulation models (2013)
    AGU (American Geophysical Union) | Wiley
    Details
    Publication Date: 2023-01-31
    Description: We analyze an extensive set of global coupled biogeochemical ocean circulation models. The focus is on the equatorial Pacific. In all simulations, which are consistent with observed standing stocks of relevant biogeochemical species at the surface, we find spuriously enhanced (reduced) macronutrient (oxygen) concentrations in the deep eastern equatorial Pacific. This modeling problem, apparently endemic to global coupled biogeochemical ocean circulation models, was coined “nutrient trapping” by Najjar et al. (1992). In contrast to Aumont et al. (1999), we argue that “nutrient trapping” is still a persistent problem, even in eddy-permitting models and, further, that the scale of the problem retards model projections of nitrogen cycling. In line with previous work, our results indicate that a deficient circulation is at the core of the problem rather than an admittedly poor quantitative understanding of biogeochemical cycles. More specifically, we present indications that “nutrient trapping” in models is a result of a spuriously damped Equatorial Intermediate (zonal) Current System and Equatorial Deep Jets—phenomenon which await a comprehensive understanding and have, to date, not been successfully simulated.
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER (OCEANREP)
  • 6
    facet.materialart.
    Unknown
    Effects of increased isopycnal diffusivity mimicking the unresolved equatorial intermediate current system in an earth system climate model (2013)
    AGU (American Geophysical Union) | Wiley
    Details
    Publication Date: 2024-01-16
    Description: Earth system climate models generally underestimate dissolved oxygen concentrations in the deep eastern equatorial Pacific. This problem is associated with the "nutrient trapping" problem, described by Najjar et al. [1992], and is, at least partially, caused by a deficient representation of the Equatorial Intermediate Current System (EICS). Here we emulate the unresolved EICS in the UVic earth system climate model by locally increasing the zonal isopycnal diffusivity. An anisotropic diffusivity of ∼50,000 m 2 s-1 yields an improved global representation of temperature, salinity and oxygen. In addition, it (1) resolves most of the local "nutrient trapping" and associated oxygen deficit in the eastern equatorial Pacific and (2) reduces spurious zonal temperature gradients on isopycnals without affecting other physical metrics such as meridional overturning or air-sea heat fluxes. Finally, climate projections of low-oxygenated waters and associated denitrification change sign and apparently become more plausible
    Type: Article , PeerReviewed
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER (OCEANREP)
  • 7
    facet.materialart.
    Unknown
    Changes in Arctic Stratification and Mixed Layer Depth Cycle: A Modeling Analysis (2022)
    AGU (American Geophysical Union) | Wiley
    Details
    Publication Date: 2024-02-07
    Description: Climate change is especially strong in the region of the Arctic Ocean, and will have an important impact on its thermo-haline structure. We analyze the results of a hindcast simulation of a new 3D ocean model of the Arctic and North Atlantic oceans for the period 1970–2019. We compared the time period 1970–1999 with the time period 2010–2019. The comparison showed that there is a decrease of stratification between the two periods over most of the shallow Arctic shelf seas and in the core of the Transpolar Ice Drift. Fresh water inputs to the ocean surface decline, and inputs of momentum to the ocean increase, which can explain the decrease in stratification. The comparison also showed that the mixed layer becomes deeper during winter, in response to the weakened stratification owing to increased vertical mixing. The comparison of summer mixed layer depths between the two time periods follows a deepening pattern that is less evident. Regional exceptions include the Nansen Basin and the part of the Canadian Basin bordering the Canadian Archipelago, where the mixed layer shoals. Trends of freshwater fluxes imply that the changes of haline stratification in these regions are also influenced by other processes, for example, horizontal advection of fresh water, increased mixing and changes in the underlaying water masses. Runoff increase toward the Arctic Ocean can locally decrease but also increase salinity, and has an impact on stratification which can be explained by coastal dynamics. The results emphasize the non-linear nature of Arctic Ocean dynamics.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER (OCEANREP)
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...