OC 298 Lab 8 - Thermohaline Circulation

OC 298 Lab #8: Thermohaline Circulation June 2, 2023 – Due Jun 9, 2023 Names of your group members: OBSERVING THERMOHALINE CIRCULATION USING ARGO FLOATS MOTIVATION To examine how Argo float trajectories reflect features of thermohaline circulation, in particular, deep western boundary currents. See Module 7, slide 41; Module 8, slide 38. BACKGROUND The Argo float program (see module 7, slide 41) was established in 1999 to provide distributed measurements of CTD (salinity, temperature, depth) data worldwide using a network of profiling floats. The original (“core”) Argo floats profiled to 1000 m and measured only CTD. Since then core Argo float depths have increased to 2000 m. More recently biogeochemical (BGC) and Deep Argo (to 6000 m) floats have come online. BGC Argo floats measure additional properties such as O2, nitrate, optical backscatter, and pH. Deep Argo floats are designed to measure full water column CTD. While the primary mission of the floats is to acquire profiles, the drift of the floats can also provide useful information about deep ocean currents. The standard Argo float mission is a 10-day cycle, with most of the float’s time spent drifting along with deep ocean currents, followed by taking a series of measurements as it moves back up (profiles) to the ocean surface. Once the float is on the surface, it gets its location and communicates with a satellite to send its data. After that, the float sinks to a drift depth of 1000 meters for about 9 days and then the float sinks to its profile depth of 2000 meters before slowly rising to the surface while measuring conductivity, temperature, and pressure. This cycle repeats until the float dies, usually 4 – 5 years later. The Deep Argo float mission is a little different. They are designed to park about 500 m above the bottom between full ocean depth profiles. This is done to minimize the Deep Argo float drift. The idea here is to have them remain at relatively fixed locations and continue to acquire full water column CTD information.

See https://argo.ucsd.edu/ for more information. PROCEDURE: Use Argo plotting tools to examine float trajectories and profiles in the North Atlantic Ocean near Iceland and Greenland and elsewhere. Argo offers a number of ways to access and plot data. The Euro Argo Data Selection Tool linked to below is one of the easiest ways to access data. I’ve asked you to include a screenshots of a few plots below. 1. Go to https://dataselection.euro-argo.eu/ 2. This opens up on the last 10 days of float data worldwide with all active (core, BGC, and deep Argo) floats visible. The total number of floats active at this time should be around 3800. Questions: 1. Examination of types of floats and the data acquired. a. Under Network, how many floats are i. Core Argo? ii. BGC Argo? iii. Deep Argo? b. Under parameters i. What are the three most common parameters acquired? ii. How many acquire dissolved oxygen (DOXY)? iii. How many acquire pH? c. Under Deployment year i. When were the oldest floats deployed? ii. In what year does a steep drop off in active floats occur? 2. Float trajectories for “old” floats. Click on Deployment years 2010-2015. This gives us a reasonable selection of “old” floats with relatively long trajectories. a. Click on a few floats in and around the Antarctic Circumpolar Current (ACC). Then click on “Show float trajectory” to see the float’s trajectory since launch. Include a screen shot of a float in the ACC here. i. What is the general direction for their movement? ii. Does this correspond with what we talked about in class? iii. The Argo floats drift at 1000 n, above most bottom topography. Having said that, do you see any evidence of the influence of bottom topography? If so, describe where. Any surprises? iv. Next find an old float in the Antarctic Circumpolar Current and click on “Show profile data” What color is the salinity profile? An orange salinity profile indicates the data have failed quality control. This is typical for the old floats – the CTD has drifted out of calibration or become fouled over the years.