Page 36: of Marine Technology Magazine (November 2018)

DEEP UNDERCURRENTS

Careful processing of LADCP data sea change. Deep current pro? ling was

A key motivation for knowing more incorporates various inputs. Current available to a much larger community. about deep currents is to clarify the pro? les from ship-mounted ADCPs are Data collection was regular and wide- global thermohaline circulation. Along used to validate LADCP pro? les where spread. And supplementary informa- they overlap. Corrections are made for tion about deep currents informed other the western edge of all major ocean ba- sins, narrow, swift undercurrents have ship’s drift and the varying attitude and studies, such as tracer measurements.

been observed at depth. They have dis- motions of the lowered package. Near LADCPs gained traction on hydro- the bottom of the cast, acoustic echoes graphic cruises during the World Ocean tinct water properties and ? ow counter to strong surface currents. scattered by the seabed reveal the AD- Circulation Experiment (WOCE, 1990-

Using LADCPs off southern Africa,

CP’s motion. Often, dual ADCPs are 2002). By the early 2000s, improved

UK scientists identi? ed an unknown un- used—looking up and down. LADCP data quality came from im-

One key advantage of the LADCP proved methods of measurement and dercurrent. The substantial Agulhas Un- method is that it does not add to ship processing. And the last two decades dercurrent, which surprisingly is not ev- time and running costs; the velocity have seen routine use of the LADCP ident in hydro data, ? ows equatorward at 1200 m depth. Found alongside the pro? le is completed during scheduled method around the global ocean. continental slope, this deep current car- hydro casts. Specialized technicians are Extensive collections of these full- not required although successfully op- depth measurements are available. And ries ten times the volume of the world’s erating the LADCP entails training and accumulating LADCP sections from largest river. Later studies con? rmed the

Undercurrent’s discovery and its unex- diligence. The ADCP’s compass should many cruises opened the door to statisti- pected water properties.

be calibrated carefully. cal descriptions. In short, LADCPs pro-

Many of these undercurrents hug the vide a unique and developing view for steep topography of the continental studying the global ocean—from large-

WINDS OF CHANGE slope. At these sites, full-depth LAD-

Adding ADCPs to hydro casts caused a scale circulation to small-scale mixing.

Fig. 2

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