Expedition 378 methods

ments."These advancements are numbered sequentially from the top of the hole downward.Numbers assigned to physical cores correspond to advancements and may not be consecutive. Drilling disturbanceCores may be significantly disturbed by the drilling process or contain extraneous material as a result of the coring and core handling process.In formations with loose granular layers (sand, ash, foraminifer ooze, chert fragments, shell hash, etc.), drilling circulation may allow granular material from intervals higher in the hole to settle and accumulate in the bottom of the hole.Such material could be sampled by the next core.Therefore, the uppermost 10-50 cm of each core must be assessed for potential "fall-in."Common coring-induced deformation includes the concave-downward appearance of originally horizontal bedding.Piston action may result in fluidization ("flow-in") at the bottom of, or sometimes in, APC cores.Retrieval of unconsolidated (APC) cores to the surface typically results to some degree in elastic rebound, and gas that is in solution at depth may become free and drive core segments in the liner apart.When gas content is high, pressure must be relieved for safety reasons before the cores are cut into segments.Holes are drilled into the liner, which forces some sediment and gas out of the liner.As noted above, XCB coring typically results in biscuits mixed with drilling slurry.RCB coring typically homogenizes unlithified core material and often fractures lithified core material.Drilling disturbances are described in Lithostratigraphy in the Site U1553 chapter (Röhl et al., 2022a) and are indicated on graphic core summary reports, also referred to as visual core descriptions (VCDs) (see Core descriptions). Seawater sampling strategySamples for phytoplankton and seawater analysis were collected from international waters during the transit from Site U1553 to Papeete (between 38°37.841′Sand 25°36′S) to assess seawater geochemistry and the abundance of coccolithophores, foraminifers, and microplastics across a South Pacific Ocean transect.Filtered seawater samples were stored for shore-based geochemical analysis and for analysis of shipboard pH, alkalinity, major ions, nutrients, and major elements.