PhD Student Chen Xu Completes First Research Cruise Aboard RRS James Cook

Our final-year PhD student, Chen Xu, has recently returned from his first research cruise, JC269, aboard the RRS James Cook. The 30-day expedition to the Iceland Basin, which took place from September 6^th to October 6^th, was part of the NERC-funded BIO-Carbon Programme. This programme aims to enhance our understanding of marine life's role in predicting future ocean carbon storage.

As the only paleoceanographer on this modern oceanographic cruise, Chen collaborated closely with other scientists onboard. He used bongo plankton nets to collect planktonic foraminifera and employed a stainless steel CTD (Conductivity, Temperature, Depth) for in-situ seawater carbonate chemistry measurements.

Boron isotope ratios (δ¹¹B) in planktonic foraminiferal shells are useful for estimating past oceanic pH and CO₂ levels, which are essential for understating the ocean's influence on the global carbon cycle and climate. The effectiveness of this proxy is often limited by species-specific "vital effects" in biomineralisation and the habitat distribution of foraminifera, necessitating precise and species-specific calibrations.

Chen's research focuses on Neogloboquadrina pachyderma, a species dominant in polar and subpolar oceans that exhibits notable pH sensitivity in its δ¹¹B composition, as indicated by previous core-top studies. However, existing relationships are based on a limited number of data points from variable, late-Holocene sediment material and climatological ocean CO₂ system data, with uncertain corrections for anthropogenic carbon.

By advancing δ¹¹B analysis and expanding the dataset—critically enhanced through improved in-situ foraminifera collection and precise seawater carbonate chemistry measurements—Chen aims to substantially reduce uncertainties in current calibrations. This integration of modern oceanography and paleoceanography is expected to enhance calibration accuracy, thereby improving reconstructions of the past oceanic CO₂ system. His work will help develop more precise and accurate predictions of climate change and oceanic carbon storage.

Beyond his primary research, Chen actively participated in various onboard experiments. He assisted with chlorophyll measurements and conducted FlowCam analyses of phytoplankton and zooplankton from seawater samples and other onboard experiments, such as those involving iron and manganese injections and respiration studies.

"This cruise was a great opportunity for me," Chen reflects. "Not only did it allow me to gather essential samples for my own paleoceanographic research, but it also provided invaluable training and offered a fresh perspective on how modern oceanographers approach carbon sequestration."

We congratulate Chen on his successful expedition and look forward to the valuable insights his research will bring to our understanding of ocean carbon storage.