NSFGEO-NERC: Using Time-series Field Observations to Constrain an Ocean Iron Model

Iron is an essential nutrient for the growth of phytoplankton in the oceans. As such, iron plays key roles in regulating marine primary production and the cycling of carbon. It is thus important that models of ocean biology and chemistry consider iron, in order to explore past, present and future variations in marine productivity and the role of the ocean in the global carbon cycle. In this joint project involving researchers in the U.S. and the U.K., supported by both NSF and the Natural Environment Research Council (U.K.), field data from the Bermuda Atlantic Time-series Study (BATS) region will be combined with an established, state-of-the-art ocean biogeochemical model. By leveraging the known seasonal-scale physical, chemical and biological changes in the BATS region, the oceanographic context provided by the BATS core data, and an existing model of the regional physical circulation, the proposed study will yield process-related information that is of general applicability to the open ocean. In particular, the proposed research will focus on understanding the atmospheric input, biological uptake, regeneration and scavenging removal of dissolved iron in the oceanic water column, which have emerged as major uncertainties in the ocean iron cycle. The project will include significant educational and training contributions at the K-12, undergraduate, graduate and postdoctoral levels, as well as public outreach efforts that aim to explain the research and its importance.

The ability of ocean models to simulate iron remains crude, owing to an insufficient understanding of the mechanisms that drive variability in dissolved iron, particularly the involvement of iron-binding ligands, colloids and particles in the surface input, biological uptake, regeneration and scavenging of dissolved iron in the upper ocean. Basin-scale data produced by the GEOTRACES program provide an important resource for testing and improving models and, by extension, our mechanistic understanding of the ocean iron cycle. However such data provide only quasi-synoptic 'snapshots', which limits their utility in isolating and identifying the processes that control dissolved iron in the upper ocean. The proposed research aims to provide mechanistic insight into these governing processes by combining time-series data from the BATS region with numerical modeling experiments. Specifically, seasonally resolved data on the vertical (upper 2,000 meters) and lateral (tens of kilometers) distributions of particulate, dissolved, colloidal, soluble and ligand-bound iron species will be obtained from the chemical analysis of water column samples collected during five cruises, spanning a full annual cycle, shared with the monthly BATS program cruises. These data, along with ancillary data from the BATS program, will be used to test and inform numerical modeling experiments, and thus derive an improved understanding of the mechanisms that control the distribution and dynamics of dissolved iron in the oceanic water column.

The proposed research will facilitate an improved mechanistic representation of iron in ocean models used for studies of marine ecology and global climate, beyond that afforded by the quasi-synoptic data from the GEOTRACES program section cruises. The project will also include education and training contributions at the undergraduate, graduate and postdoctoral levels, and outreach activities focusing on high-school students and the general public. A graduate student at the University of South Florida will be co-supervised by PIs Buck and Sedwick, with Buck acting as primary academic supervisor. This MS or PhD student will receive training in trace metal clean sampling and analyses, will participate in the project cruises, and the proposed speciation analyses will form the basis of their thesis or dissertation research. In addition, an early-career researcher (Ohnemus) and a postdoctoral fellow at the University of Liverpool (to be determined) will be supported. Co-PI Johnson is lead instructor for the joint BIOS-Dalhousie Sea Experience in Shipboard Oceanography program, in which he will supervise graduate students (8-12 per year) on BATS cruises to further their research. Two undergraduate research interns will be engaged at Bigelow, one through the institute's summer REU program, and one Colby College student through the Changing Oceans semester-in-residence program. Co-PI Buck continues to serve as a mentor for the Oceanography Camp for Girls program hosted by the USF College of Marine Science, which brings incoming high school students to USF for three weeks of interactive, hands-on experience in oceanography. As a part of their experience, these young women have a chance to interview Buck and other marine science faculty about their education, career paths and ongoing research. Buck's lab will also design a hands-on chemistry lab to highlight project activities for Oceanography Camp for Girls and incorporate these activities into a booth at the St. Petersburg Science Festival, an annual 2-day open house outreach event that aims to expose school groups and the public to science.