High concentrations of trace metals in the environment can be deadly to life but most life cannot thrive without small quantities of elements such as iron and zinc. This is why we study the chemistry of these metals in the ocean.
Iron is an essential nutrient for phytoplankton growth in the ocean. Phytoplankton are at the base of the food chain in ocean ecosystems but also photosynthesise and use up carbon dioxide in the ocean so the amount that these organisms can grow has important implications for the linked ocean-atmosphere system. Knowing how iron is supplied to the oceans and how this has changed in the past will help us to make better predictions about how our environment may change in the future.
Iron is only present in extremely small concentrations in the ocean due to its low solubility in oxic seawater. This means that in some regions of the ocean the lack of iron limits phytoplankton growth. In order to understand why some regions of the ocean are iron-limited, the potential sources of iron need to be sampled to examine how this element behaves in the environment.
The rear view of the ROV with
the niskin bottles mounted on the
port side. We use these to sample
water close to the vents.
Due to the low concentrations of iron we are dealing with, samples are very easily contaminated. Certain precautions have to be taken to make sure we are measuring the actual concentration of iron in the water that was sampled.
The first step to prevent contamination of any samples begins weeks before any research cruise starts. The plastic bottles used to store samples may look clean and new, but they can contain particles which may spoil samples, and to remove absolutely everything the bottles need to be washed in baths of acid for weeks. Washing hundreds of plastic bottles in acid was my very first task upon starting my PhD last October.
|Aly sampling the CTD|
|Left to right: filtering from niskin bottles under pressure from nitrogen line., vacuum pump filtering, pre-rinsing of 0.02µm filters for in-line filtering|
By A.J. Mackenzie Lough