Patrick Wetzel - Academia.edu (original) (raw)

Papers by Patrick Wetzel

Abstract Trends and variability in the ocean-atmosphere CO2-flux and the uptake of anthropogenic ... more Abstract Trends and variability in the ocean-atmosphere CO2-flux and the uptake of anthropogenic CO2 are simulated for the period 1948-2003, using a biogeochemical carbon cycle model (HAMOCC5) coupled on-line to a global Ocean General Circulation Model ( ...

A carbon cycle model embedded in a state-of-the-art ocean general circulation and sea ice model h... more A carbon cycle model embedded in a state-of-the-art ocean general circulation and sea ice model has been applied to quantify the important mechanisms of the interannual and decadal sea- to-air CO 2 flux variability and the variations in the uptake of anthropogenic CO 2 . The model is forced by daily NCEP/NCAR reanalysis data over a 56 year period of time, showing trends and variability on interannual and decadal scales. The total interannual variability of the model is ±0.50 Pg C yr -1 , confirming estimates from previous studies. This is largely dominated by ocean dynamics in the equatorial Pacific, where changes in air-to-sea CO 2 fluxes have a variability of ±0.33 Pg C yr -1 and are characterized by wind stress-induced changes in the surface dissolved inorganic carbon concentration. We estimate an average CO 2 flux into the ocean of -1.74 Pg C yr -1 for the period between 1990 and 2000, with extremes of -1.20 Pg C yr -1 at the La Niña in 1996 and -2.10 Pg C yr -1 flux during the ...

Journal of Climate, 2006

The influence of phytoplankton on the seasonal cycle and the mean global climate is investigated ... more The influence of phytoplankton on the seasonal cycle and the mean global climate is investigated in a fully coupled climate model. The control experiment uses a fixed attenuation depth for shortwave radiation, while the attenuation depth in the experiment with biology is derived from phytoplankton concentrations simulated with a marine biogeochemical model coupled online to the ocean model. Some of the changes in the upper ocean are similar to the results from previous studies that did not use interactive atmospheres, for example, amplification of the seasonal cycle; warming in upwelling regions, such as the equatorial Pacific and the Arabian Sea; and reduction in sea ice cover in the high latitudes. In addition, positive feedbacks within the climate system cause a global shift of the seasonal cycle. The onset of spring is about 2 weeks earlier, which results in a more realistic representation of the seasons. Feedback mechanisms, such as increased wind stress and changes in the shor...

Climate Dynamics, 2008

The increase of atmospheric CO 2 concentrations due to anthropogenic activities is substantially ... more The increase of atmospheric CO 2 concentrations due to anthropogenic activities is substantially damped by the ocean, whose CO 2 uptake is determined by the state of the ocean, which in turn is influenced by climate change. We investigate the mechanisms of the ocean's carbon uptake within the feedback loop of atmospheric CO 2 concentration, climate change and atmosphere/ocean CO 2 flux. We evaluate two transient simulations from 1860 until 2100, performed with a version of the Max Planck Institute Earth System Model (MPI-ESM) with the carbon cycle included. In both experiments observed anthropogenic CO 2 emissions were prescribed until 2000, followed by the emissions according to the IPCC Scenario A2. In one simulation the radiative forcing of changing atmospheric CO 2 is taken into account (coupled), in the other it is suppressed (uncoupled). In both simulations, the oceanic carbon uptake increases from 1 GT C/year in 1960 to 4.5 GT C/year in 2070. Afterwards, this trend weakens in the coupled simulation, leading to a reduced uptake rate of 10% in 2100 compared to the uncoupled simulation. This includes a partial offset due to higher atmospheric CO 2 concentrations in the coupled simulation owing to reduced carbon uptake by the terrestrial biosphere. The difference of the oceanic carbon uptake between both simulations is primarily due to partial pressure difference and secondary to solubility changes. These contributions are widely offset by changes of gas transfer velocity due to sea ice melting and wind changes. The major differences appear in the Southern Ocean (-45%) and in the North Atlantic (-30%), related to reduced vertical mixing and North Atlantic meridional overturning circulation, respectively. In the polar areas, sea ice melting induces additional CO 2 uptake (+20%). Keywords Ocean carbon cycle Á Climate change Á Ocean circulation Á Climate scenarios Á Air-sea CO 2 flux Clim Dyn

Working Papers, Feb 1, 2005

Terrestrial sinks have entered the Kyoto Protocol as offsets for carbon sequestration, but ocean ... more Terrestrial sinks have entered the Kyoto Protocol as offsets for carbon sequestration, but ocean sinks have escaped attention. Ocean sinks are as unexplored and uncertain as were the terrestrial sinks at the time of negotiation. It is not unlikely that certain countries will advocate the inclusion of ocean carbon sinks to reduce their emission reduction obligations. We use a simple model of the international market for carbon dioxide emissions to evaluate who would gain or loose from allowing for ocean carbon sinks. Our analysis is restricted to information on anthropogenic carbon sequestration within the exclusive economic zone of a country. Like the carbon sequestration of business as usual forest management activities, natural ocean carbon sequestration applies at zero costs. The total amount of anthropogenic ocean carbon sequestration is large, also in the exclusive economic zones. As a consequence, it substantially alters the costs of emission reduction for most countries. Countries such as Australia,

Global Biogeochemical Cycles, 2005

The interannual variability of atmospheric CO 2 growth rate shows remarkable correlation with the... more The interannual variability of atmospheric CO 2 growth rate shows remarkable correlation with the El Niño Southern Oscillation (ENSO). Here we present results from mechanistically based terrestrial carbon cycle model VEgetation-Global-Atmosphere-Soil (VEGAS), forced by observed climate fields such as precipitation and temperature. Land is found to explain most of the interannual CO 2 variability with a magnitude of about 5 PgC yr À1. The simulated land-atmosphere flux has a detrended correlation of 0.53 (0.6 at the 2-7 year ENSO band) with the CO 2 growth rate observed at Mauna Loa from 1965 to 2000. We also present the total ocean flux from the Hamburg Ocean Carbon Cycle Model (HAMOCC) which shows ocean-atmosphere flux variation of about 1 PgC yr À1 , and it is largely out of phase with land flux. On land, much of the change comes from the tropical regions such as the Amazon and Indonesia where ENSO related climate anomalies are in the same direction across much of the tropics. The subcontinental variations over North America and Eurasia are comparable to the tropics but the total interannual variability is about 1 PgC yr À1 due to the cancellation from the subregions. This has implication for flux measurement network distribution. The tropical dominance also results from a ''conspiracy'' between climate and plant/soil physiology, as precipitation and temperature changes drive opposite changes in net primary production (NPP) and heterotrophic respiration (R h), both contributing to land-atmosphere flux changes in the same direction. However, NPP contributes to about three fourths of the total tropical interannual variation and the rest is from heterotrophic respiration; thus precipitation appears to be a more important factor than temperature on the interannual timescales as tropical wet and dry regimes control vegetation growth. Fire, largely driven by drought, also contributes significantly to the interannual CO 2 variability at a rate of about 1 PgC yr À1 , and it is not totally in phase with NPP or R h. The robust variability in tropical fluxes agree well with atmospheric inverse modeling results. Even over North America and Eurasia, where ENSO teleconnection is less robust, the fluxes show general agreement with inversion results, an encouraging sign for fruitful carbon data assimilation.

Geochimica et Cosmochimica Acta, 2006

The increase of atmospheric CO 2 due to anthropogenic activity is substantially damped by CO 2 fl... more The increase of atmospheric CO 2 due to anthropogenic activity is substantially damped by CO 2 fluxes into the ocean. Besides the atmospheric CO 2 concentration, the uptake depends on the state of the ocean, which in turn is influenced by climate change. Here, we assess the response of future oceanic CO 2 uptake to climate change. For that reason we evaluate two simulations of a version of the Max Planck Institute Earth System Model (MPI-ESM), consisting of the atmosphere, the ocean with biogeochemistry and land surface performed from 1860 until 2100. Both simulations are driven with observed CO 2 emissions between 1860 until 2000. Afterwards the CO 2 emissions of the IPCC scenario A2 are assumed. Whereas one simulation allows the feedback between atmospheric CO 2 concentration and climate, the other artificially surpresses it. Both simulations show a nearly linearly increased CO 2 uptake of the oceans from 1960 until around 2070 to about 4.5 GT/yr. From then on, the rise of the globally integrated uptake in the climate change run strongly weakens, leading to a difference uptake rate between the two runs of about 10% at the end of the 21st century. The spatial distribution of the uptake difference between the two runs shows a pronounced pattern: In the North Atlantic and south of South America the ocean CO 2 uptake is clearly reduced in the climate change run. Smaller decreases are found in the tropical oceans. However, there are some parts of the oceans, e.g. the polar areas, where the flux into the ocean is further increased. The potential reasons for the spatially different CO 2-flux responses to climate change are discussed.