ALBERT

Description: The workshop on polar lows (PLs) and mesoscale weather extremes attracted 30 scientists from China, France, Germany, Japan, Norway, Russia, the United Kingdom, and the United States to present the most recent findings on PL research and to summarize our present understanding of PLs and mesocyclones (MCs) as well as mesoscale weather extremes in the Arctic and Antarctic (see sidebar for the definition of PLs). The workshop had the following main themes: PL studies using satellite data and in situ observations, climatological aspects, PLs in reanalyses and model simulations, environments for PL genesis and operational aspects, polar mesoscale weather phenomena, and air–ocean–ice interactions. The workshop was concluded by a roundtable discussion resulting in recommendations for future research and actions.

Description: The Water and Global Change (WATCH) forcing datasets have been created to support the use of hydrological and land surface models for the assessment of the water cycle within climate change studies. They are based on 40-yr ECMWF Re-Analysis (ERA-40) or ECMWF interim reanalysis (ERA-Interim) with temperatures (among other variables) adjusted such that their monthly means match the monthly temperature dataset from the Climatic Research Unit. To this end, daily minimum, maximum, and mean temperatures within one calendar month have been subjected to a correction involving monthly means of the respective month. As these corrections can be largely different for adjacent months, this procedure potentially leads to implausible differences in daily temperatures across the boundaries of calendar months. We analyze day-to-day temperature fluctuations within and across months and find that across-months differences are significantly larger, mostly in the tropics and frigid zones. Average across-months differences in daily mean temperature are typically between 10% and 40% larger than their corresponding within-months average temperature differences. However, regions with differences up to 200% can be found in tropical Africa. Particularly in regions where snowmelt is a relevant player for hydrology, a few degrees Celsius difference can be decisive for triggering this process. Daily maximum and minimum temperatures are affected in the same regions, but in a less severe way.

Description: Dates of Cruise: 15.09. to 18.09.2003 Projects: BASEWECS and Student course in physical oceanography; Port Calls: Warnemünde (15.09. and 18.09.2003)

Description: Dates of Cruise: 07.07. - 09.07.2003 Projects: BASEWECS and Student course in physical oceanography; Port Calls: Warnemünde, 07.07.-08.07.2003

Description: The impact by freshwater and marine mesozooplankton on phytoplankton particle size and stoichiometry was studied. Additionally, zooplankton d15N were determined as an inidicator of trophic level. Mesocosm studies, using logarithmically scaled zooplankton density gradients, were performed at three locations (lake Schoehsee, the marine Hopavagen lagoon, Norway, and Kiel Fjord) in August 2000, July 2001 and September 2002. In two of the three studies (Schoehsee, Hopavagen), zooplankton shifted phytoplankton size structure predictably to small or large species, respectively, with freshwater zooplankton (copepods, Daphnia) being complementary in their impact. Stoichiometrically, both Daphnia and marine copepods increased the carbon to nutrient ratios (C:P or C:N) of POM, indicative of phytoplankton nutrient limitation. Yet, while the depletion of P in freshwater POM was due to its retention in ‘new’ Daphnia biomass (numerical increase), the mechanism for marine copepods was different: copepods triggered the growth of nanoflagellates via a a trophic cascade (‘copepods-ciliates-nanoflagellates’), which increased at the expense of their intracellular nitrogen pool. Measurements of zooplankton d15N showed that differences were large between Daphnia and freshwater copepods (3.2 to 4.8‰), while negligible between marine copepods and the appendicularian Oikopleura dioica. Moreover, stable isotope analysis revealed different patterns of d15N enrichment for cruising versus stationary suspension feeding copepods, and also traced the (indirect) transfer of isotopically ‘light’ nitrogen from diazotrophic cyanobacteria to zooplankton.