E. Zorita

Unsaturated fatty acid content in seston and tropho-dynamic coupling in lakes

Determining the factors that control food web interactions is a key issue in ecology. The empirical relationship between nutrient loading (total phosphorus) and phytoplankton standing stock (chlorophyll a) in lakes was described about 30 years ago and is central for managing surface water quality. The efficiency with which biomass and energy are transferred through the food web and sustain the production of higher trophic levels (such as fish) declines with nutrient loading and system productivity, but the underlying mechanisms are poorly understood. Here we show that in seston (fine particles in water) during summer, specific ω3-polyunsaturated fatty acids (ω3-PUFAs), which are important for zooplankton, are significantly correlated to the trophic status of the lake. The ω3-PUFAs octadecatetraenoic acid, eicosapentaenoic acid (EPA) and docosahexaenoic acid, but not α-linolenic acid, decrease on a double-logarithmic scale with increasing total phosphorus. By combining the empirical relationship between EPA-to-carbon content and total phosphorus with functional models relating EPA-to-carbon content to the growth and egg production of daphnids, we predict secondary production for this key consumer. Thus, the decreasing efficiency in energy transfer with increasing lake productivity can be explained by differences in ω3-PUFA-associated food quality at the plant–animal interface.

Deep soil temperature as proxy for surface air‐temperature in a coupled model simulation of the last thousand years

[1]xa0The relationship between terrestrial deep soil temperature (TDST) and surface temperature (SAT) at interannual and centennial timescales has been investigated in a simulation of the last millennium with a three-dimensional climate model driven by estimations of historical external forcing. TDST is loosely related to borehole temperature profiles, which have been recently used to reconstruct long term temperature trends in the last centuries. Recently, questions about the validity of boreholes-based reconstructions have been raised. In the simulation, at interannual time scales the connection between TDST and SAT is stable, being stronger in the summer half year than in the winter half year. At long timescales, annual TDSL is a good proxy for annual SAT, and their variations are almost indistinguishable from each other. Both TDSL and terrestrial SAT overestimate the variations of global mean SAT. This may be a source for the disagreement between statistical reconstructions of global SAT and terrestrial borehole measurements.

Natural and anthropogenic modes of surface temperature variations in the last thousand years

The spatial patterns of surface air-temperature variations in the period 1000 to 2100, simulated with the ECHO-G atmosphere-ocean coupled model, are analyzed. The model was driven by solar, volcanic and greenhouse gas forcing. The leading mode of temperature variability in the preindustrial period represents an almost global coherent variation of temperatures, with larger amplitudes over the continents and Northern Hemisphere. This mode also describes a large part of the spatial structure of the warming simulated in the 21st century. However, in the 21st century, regional departures from this spatial structure are also present and can be ascribed to atmospheric circulation responses to anthropogenic forcing in the last decades of the 21st century.

IPCC: cherish it, tweak it or scrap it?

As calls for reform intensify following recent furores about e-mails, conflicts of interest, glaciers and extreme weather, five climatologists propose ways forward for the Intergovernmental Panel on Climate Change. Their suggestions range from reaffirming the panel governing principles to increasing the number and speed of its publications to replacing the volunteer organization with a permanently staffed structure.

How unusual is the recent series of warm years

[1]xa0Previous statistical detection methods based partially on climate model simulations indicate that, globally, the observed warming lies very probably outside the natural variations. We use a more simple approach to assess recent warming at different spatial scales without making explicit use of climate simulations. It considers the likelihood that the observed recent clustering of warm record-breaking mean temperatures at global, regional and local scales may occur by chance in a stationary climate. Under two statistical null-hypotheses, autoregressive and long-memory, this probability turns to be very low: for the global records lower than p = 0.001, and even lower for some regional records. The picture for the individual long station records is not as clear, as the number of recent record years is not as large as for the spatially averaged temperatures.

Comment on ‘Improved global maps and 54‐year history of wind‐work on ocean inertial motions’ by M. H. Alford

In his paper Improved global maps and 54-year history of wind-work on ocean inertial motions, the author is using near surface (10 meter) winds from a number of different sources as input for subsequent analyses. One of the sources is the gridded multi-decadal reconstruction prepared by Feser et al. (2001) with the help of the regional atmospheric model REMO (Jacob et al., 1995). Another source used are the NCEP reanalyses (Kalnay et al., 1996). Analyzing both types of data Alford (2003) comes to the conclusion that The NCEP and the REMO winds are highly coherent at all frequencies over the entire domain. However, the spectra of the REMO winds at ƒ are lower than the NCEP winds by a constant factor. To account for this attenuation, the REMO winds are multiplied by 1.32. This conclusion is based on the fact that a comparison of NCEP spectra with buoy data in the Pacific yields good agreement and that a visual comparison of spectra obtained from REMO and NCEP wind fields showed a clear underestimation at high frequencies for the REMO winds (Alford 2003, pers. comm.). We tried to reconstruct the spectra that led Alford (2003) to the conclusion that REMO winds have too little variance at high frequencies. In Figure 1 spectra of the zonal wind component at 10 m height are shown for hourly sampled REMO and 6-hourly sampled NCEP winds. In addition a spectrum of 6-hourly sampled REMO winds is shown. While all three spectra agree well at low frequencies there is indeed discrepancy between the 6-hourly sampled NCEP (black curve) and the hourly sampled REMO winds (blue curve) at the high-frequency end of the spectrum. If the hourly REMO time-series is sampled at 6-hour intervals (red line), the resemblance with NCEP in the high-frequency range is obvious. This suggests that the hourly sampled REMO winds do not underestimate spectral densities but that the 6-hourly sampled data suffer from an aliasing effect In such cases, variations at time scales shorter than the Nyquist folding frequency (2∆)-1 (where ∆ represents the sampling interval), are folded onto the resolved frequencies. A poor choice of sampling intervals can obviously lead to non-fitting spectra and misleading interpretation. In fact, multiplication of the hourly REMO winds by a factor of 1.32 artificially raises the spectral levels at high frequencies close to those obtained from 6-hourly sampled NCEP (and REMO) data but in the same …

An attempt to deconstruct recent climate change in the Baltic Sea basin

We investigate whether the recently observed temperature and precipitation trends over the Baltic Sea Basin are consistent with state-of-the-art regional climate model projections. To address this question we use several data sources: 1) multi-decadal trends derived from various observational data sets, 2) estimates of natural variability provided by a 2,000-year paleoclimatic model simulation, and 3) response to greenhouse gas forcing derived from regional climate simulations driven by the A1B and RCP4.5 scenarios (from ENSEMBLES and CORDEX projects). n nResults indicate that, over the past decades, the climate in the Baltic Sea Basin has undergone a change that is beyond the estimated range of natural variability. We test the hypothesis that this change may be understood as a manifestation of global warming due to increasing concentrations of greenhouse gases (GHGs). We find that changes in near-surface temperature support our hypothesis that the effect of GHG is needed to simulate the observed changes. The pattern correlation and regression results clearly illustrate the concerted emergence of an anthropogenic signal consistent with the GHG signal in summer and autumn in the 21st century. However, none of the 19 regional climate simulations used in this study reproduce the observed warming. The observed trends in precipitation and surface solar radiation are also partially inconsistent with the expected changes due to GHG forcing. We conclude that, besides the regional response to GHG forcing, other human-made drivers have had an imprint. Regional emission of industrial aerosols has been strongly reduced in this region, and we suggest that this reduction may be the missing driver.

Coral Climate History of the Subtropical North Atlantic (CorClim)

Introduction There are only a few high-resolution proxy records of North Atlantic climate variability and associated teleconnection patterns (e.g. Kuhnert et al., 2002). The generation of additional data that extend beyond the period of instrumental measurements at key locations is essential to improve climate reconstructions. Bermuda represents such a key location. The region is sensitive to North Atlantic Oscillation (NAO) variability, where the NAO infl uence is exerted by local air-sea interactions as well as by largescale changes in the circulations of the Gulf Stream and the North Atlantic Subtropical Gyre. Bermuda also represents the northernmost site in the Atlantic Ocean where climate records can be recovered from stony reef corals. Here we investigate two coral specimens (Montastrea cavernosa, Diploria strigosa) from Bermuda, collected at the same site and depth (12m). The data include monthly Sr/Ca ratios from Diploria and annual skeletal growth rates from both species, extending back from 1983 to 1929 and 1842, respectively. Therefore, instrumental as well as pre-instrumental times are represented by the corals, which makes it possible to calibrate against instrumental data.