Headed for Home Port

Rick Murray, Chief Scientist

I’m typing this while we are just southwest of Martha’s Vineyard, and will be heading into Woods Hole in the early morning tomorrow (Wednesday, December 3).  On board all scientific measurements are completed, reports are written, the laboratories and coring equipment are essentially packed, and many of us are looking forward to reaching shore tomorrow morning.  People are relaxed, tired, happy and satisfied at work well done, and partially sad that the cruise is winding up.

For this final blog post, I felt it appropriate to share a “Dedication” with which our science party prefaced our Cruise Report, and the “Executive Summary” of the Cruise Report as well.

Thanks for visiting along with us during our research cruise.  Stay tuned for more great science to come from it!

Dedication

This cruise is the last full research expedition of the venerable and eminent R/V Knorr.  As the last full complement of scientists to sail with her, it has been our privilege to share this ride.  In admiration and respect for the men and women who have journeyed with her as crew, technicians, scientists, and visitors over the past 40 years, we dedicate this Cruise Report to the spirit of exploration, scientific inquiry, and the pursuit of excellence that the R/V Knorr has exemplified for so many days, nights, and miles traversing the vast unknowns of the sea.

Executive Summary

During Cruise KN-223 we successfully gathered 10 Multicores, 18 Gravity Cores, and 12 Long Cores from 16 different stations throughout the western North Atlantic Ocean.  We occupied sites ranging in latitude from the Researcher Ridge (~ 15o N) to the Sohm Abyssal Plain and northern Bermuda Rise (~ 35o N).

We successfully achieved our primary and most important goal, namely, of collecting sedimentary porewaters and making geochemical measurements of sufficient fidelity to prove the porewater’s utility in unraveling the paleo-ocean chemistry of bottom water during the Last Glacial Maximum.  Our stations, several of which were identified during the cruise itself, were strategically located to investigate meridional gradients in bottom water chemistry and physical properties.  Our deepest water sites also fulfilled a prime objective of sampling pelagic sediment that seems to be completely oxygenated from the seafloor to the basaltic basement, which will allow the reconstruction of nutrient utilization during the Last Glacial Maximum.  This range of oxygenation will also provide further materials for pathfinding research into subseafloor microbial energetics.

Our geochemical focus resulted in gathering sediment porewaters using strategies tailored for the different targeted chemical species.  These strategies resulted in 386 samples being squeezed for porewaters that were distributed into 2,625 different aliquots for shipboard and shorebased analyses, and 427 different in situ Rhizon samples resulting in an additional 1,752 porewater aliquots for shipboard and shorebased analyses.  Our shipboard analytical protocols included a novel approach to measuring the density of porewaters using a method that has never been attempted before for porewaters anywhere, let alone at sea in near real time.  Other measurements were performed to standards of precision and accuracy that are unprecedented, reflecting the collected experience and continual evolution of our analytical teams.

In our quest to locate adequate shallow water coring locations along the Researcher Ridge, we also performed detailed mapping that yielded surprising data germane to developing an improved understanding of this feature that is located along the North Atlantic-South Atlantic plate boundary.  While we failed in our goal to find appropriate shallow water sites to core, the geological and geophysical knowledge gained during this surveying has the potential to contribute significantly to discussions regarding the response of plate boundaries to changes in spreading directions and the synchronous or asynchronous generation of magma in regions of ocean crustal extension along boundaries that are perpendicular to ridge axes.

To serve our colleagues at the NOSAMS Facility at WHOI and therefore the oceanographic community at large, we also on two occasions gathered significant volumes of deep water for use as radioisotope standards.  Our last coring station was added late in the cruise to gather sediment at a key location for study of deep-water changes by the sedimentary paleoceanographic community.  Finally, we coordinated our coring calendar and cruise track to rescue a malfunctioning Slocum glider on behalf of Rutgers University and the US Navy.