SOLAS Acterberg NE/C00193/1

There are strong signals that suggest that our climate is changing. The emission of greenhouse gases, like carbon dioxide and methane, are changing global temperatures and weather patterns. The strong rise in atmospheric carbon dioxide concentrations over the last 100 years is caused by an increased use of fossil fuels. The ocean is a very important global storage reservoir for atmospheric carbon dioxide. However, the transfer of this gas from the atmosphere to the ocean is rather slow. Tiny microscopic plants in the oceans, including phytoplankton and bacterioplankton, play an important role in taking up carbon dioxide. Upon their death, a part of their population will sink to deep waters and sediments, and hence transfer carbon dioxide from the atmosphere to deep ocean environments. In the deep ocean the carbon will remain for a long period of time, and therefore this part of the ocean is an important long term storage reservoir. The growth of the phytoplankton and bacterioplankton is very slow, especially in ocean regions very far from land. Just like plants in gardens and agricultural fields, they require nutrients to increase their growth rate. The nutrients include nitrogen, phosphorus and trace metals like iron and zinc. These elements occur at such low concentrations in oceanic surface waters that they limit optimal growth of photosynthesising organisms. An important transport route to the open ocean for these nutrients is the atmosphere. Dust from the Saharan desert is transported over large distances and is deposited in the ocean, with the tropical North Atlantic Ocean receiving an important share of the Saharan material. The dust releases a small amount of nutrients after it is deposited in the surface ocean. This supply of nutrients is essential for the growth of phytoplankton and bacterioplankton as they receive only small amounts from other sources. We know very little about the amounts of dust falling into the ocean, the amounts of nutrients that come off the dust, and the effects that these nutrients have on the growth of organisms in the ocean. In addition, strong temporal and spatial changes occur in dust deposition, with the dust falling often in pulses during strong dust storm events. In this study we propose to undertake a research cruise in the tropical Atlantic Ocean to investigate spatial changes in atmospheric dust concentrations and their influence on nutrient concentrations in the oceanic waters. In addition, on the ship we will study the impact of dust on the microscopic organisms by undertaking growth experiments in bottles whereby we add a small amount of dust to freshly collected seawater and follow the growth of the organisms in the bottles. We will also set up a monitoring programme on Cape Verde, an island in the tropical North Atlantic which receives an important amount of Saharan dust. On the island we will determine the nutrients and metals which are delivered by the dust. We will also measure the effect that the release of nutrients from the dust has on the marine ecosystem in the sea, at a mooring site close to the island. By undertaking the fieldwork for a period of 2-3 years we hope to find out longer-term trends in the relationships between nutrient supply by dust and growth by phytoplankton and bacterioplankton. The study will therefore help us to improve our understanding of the influence of Saharan dust on the growth of oceanic plants and bacteria, and how the sporadic nature of the dust inputs affects the ecosystems. The outcomes of this research study will contribute to our understanding of the role that microscopic oceanic organisms play in the exchange of carbon dioxide between the atmosphere and the ocean, and consequently the way they can influence our climate.