The essential micronutrient iron (Fe) limits productivity in much of the global ocean. However, understanding the sensitivity of marine productivity to Fe supply is hindered by uncertainty in the residence time of Fe in the ocean, with estimates spanning two orders of magnitude. This uncertainty arises from limited knowledge of Fe inputs at ocean margins and must be addressed if we are to predict the effects of changing Fe supply to the ocean.
Ocean margin sources such as continental run-off, sediments and hydrothermal vents are key sources of iron and other essential nutrients. At many ocean margins, fluxes of trace metals are poorly constrained, owing to a lack of time information with which to accurately assess supply rates. My research uses radium isotopes, a powerful approach for constraining input and removal of Fe at different margin sources. Radium (Ra) decays over time after release from sediment, making it an ideal chronometric tracer of ocean margin processes. I will present data from recent work in the North Atlantic, combining Ra and Fe to estimate shelf and slope fluxes. This work shows that sedimentary sources are larger that we currently appreciate, and I will discuss the potential mechanisms driving this sedimentary Fe release.
Underestimated sedimentary Fe input has important consequences for our understanding of the sensitivity of the marine Fe cycle. My work suggests that processes such as accelerating glacial melt and proliferation of low-oxygen conditions will strongly impact the ocean Fe inventory. A case-study from the southwest Greenland margin will demonstrate the spatial and temporal longevity of Fe and other glacially-sources bioactive metals in this region.
Amber was first introduced to trace metals in the ocean by John Martin’s Iron Hypothesis, and famous quote “Give me half a tanker of iron and I will give you another ice age.” The idea of something as tiny as single-celled phytoplankton, and the micronutrients they depend on, affecting something as large as global climate cycles has fascinated her ever since. Starting with a BSc (Hons) degree in diatom physiology in her home town of Vancouver (Canada), she moved to MSc and PhD work in Ocean Global Change at the University of Edinburgh (UK). After spending a full year living and working in Antarctica at the British research station Rothera, she held post-doctoral research positions in Edinburgh and at Rutgers University (NJ, USA) investigating how iron accumulates in shelf seas and how this can be transferred to open-ocean waters. She has recently started a 5-year Independent Research Fellowship at the University of Southampton, establishing the UK’s largest short-lived Radium facility and joining two trans-Atlantic cruises since July 2017. Her research focuses on filling the gaps in our understanding of iron sources to the oceans.