Dataset: BVAL CTD profiles (BATS Validation cruises)

BATS Validation Cruises

Following the first several years of the BATS project it was deemed necessary by the JGOFS steering committee and BATS PI’s to conduct validation cruises in the vicinity of the nominal BATS site to better understand the mesoscale and larger scale variability of the region. In particular, a focus of the BVAL cruises was to assess the spatial scale representation of the BATS and Hydrostation ‘S’ programs. Initial focus of the BVAL cruises was to investigate mesoscale variability and  meridional gradients of the local region. Later, cruises focused on specific mesoscale eddies (e.g., Mcgillicuddy et al., 1998; McGillicuddy et al., 1999) and effects of tropical cyclones through the local region.

In 2000 it was deemed more important to document the larger scale changes in the North Atlantic Subtropical gyre and BVAL cruises established a transect line from ~ 35N to 19N (Bermuda to Puerto Rico) very similar to the WOCE A22 repeat hydrography line (Johnson et al., 2020).  These annual Bermuda to Puerto Rico transects have been run since 2000 and target stations at every one degree of latitude and typically have been conducted in September/October of each year to capture maximal heat content in the upper ocean. However, since this  timeframe coincides with high tropical cyclone activity the cruises were reluctantly (as of 2022) moved to start in June/July of each year for safety and operational reasons. In the pentad prior to 2022 every BVAL cruise was significantly impacted but multiple tropical cyclones. Parameters presented are the same as provided in the BATS standard CTD data.

BATS Validation CTD Protocol

CTD profiles for BATS validation cruises have been collected since April 1991 and although there have been some changes during this period as a result of new instrumentation or methodologies, the general sampling procedures have been consistent with those detailed in the BATS method manual version #4 (Knap et al., 1997).

In summary, the CTD is operated as per SeaBird's suggested methods with data collection at the full scan rate of 24 Hz. The CTD is powered up and allowed to stabilize at 12 m prior to profiling and once stable  (typically 4 minutes) the CTD is brought back to the surface from which point the profile begins with typical descent rates of 0.7-1.0 m/s, depending on weather conditions. Water samples are collected on the upcast and prior to triggering bottles the CTD is kept at the desired depth for a minimum of 60 seconds to ensure that entrainment from the following wake has subsided. Once the water sample is taken the CTD immediately continues with the upcast at an ascent rate of 0.7-1.0 m/s.