OC473: Eighteen tows were taken on the cruise, all successfully. The first one was at Test Station 1. Sixteen were taken at strategic locations along the 3 primary sampling transect lines (Figure 9.1). Appendix 1 gives the positions, depths, and other information for each cast. One additional tow was taken at station # 32 to the west of transect 3 in Labrador Sea water.
The MOCNESS was equipped with eight 150-um mesh nets (nets 1-8; borrowed from URI) and one 333-um mesh net (net 0). The underwater unit used was #169. In addition to the standard temperature and conductivity probes the system also had a beta-type strobe-light unit for reducing avoidance of the nets by some zooplankton and possibly small fish. The strobe system has two units each with 12 LED sets (LUXEON Rebel LED) with peak output between 490-520 nm. Seven of the 24 LED sets were no longer working at the start of the sampling. The LEDs are powered by the MOCNESS battery and their pulse width, amplitude, flash rate period, and on/off are controlled by the MOCNESS software. For this cruise the pulse width was 2 ms, the relative amplitude was 99%, and the flash interval was 100 ms.
Like the CTD, the MOCNESS was deployed from the starboard side hydroboom, but using the COM-15 oceanographic winch. Between casts it was laid down on its back on a galvanized steel stanchion installed for this purpose and tied down with ratchet straps. Having it lie on its back made cocking it very straightforward. For deployment, we used two slip-lines, one tied down to the same forward eye bolt/cleat used for the CTD and strung through the port side bottom I-beam U-bolt, and the other tied to the rail and strung through the starboard side bottom I-beam U-bolt. The system was first stood up then maneuvered such that it stood half-way out the gate; the nets were then thrown over the side in order (0 through 8), making sure to walk the forward end around the aft end of the gate to prevent the net from being snagged and torn. For recovery we use the forward air-tugger and a snap hook through the port side U-bolt and a snap hook on a line to the rail for the starboard side U-bolt. Like with the CTD, two people tended the sliplines while a third tended the conducting cable for the other oceanographic winch (attached to the CTD). In the course of recovery the system was again positioned half-way out the gate, allowing each net to be hauled on board, again making sure to avoid snagging any net on the edge of the gate. The nets were all hosed down with seawater with the system standing in this position. As each net was rinsed down the cod-ends were sequentially removed, placed in numbered buckets with two frozen cooler-packs, and transferred to the wet lab. Following this process, the system was then laid back down into the stanchion.
Oblique casts with the MOCNESS were made to 1000m with a ship speed nominally of 2 kts. Generally sampling was from 1000-800, 800-600, 600-400, 400-200, 200-100, 100-50, 50-25, 25-0m, except at test station 1 where sampling with four nets at 25 m intervals took place in the upper 100 m. The downcast started with the winch paying out at 10 m/min then at ca. 50 m the rate was increased to 20 m/min, and at ca. 100m to 30-35 m/min. Between 1500 and 2100 m were paid out to get the MOCNESS to 1000 m depending on ship speed and currents. The up-cast haul-in rate was variable, depending on the vertical velocity and how much wire was out, but was generally ca. 20 m/min below 100m and then 10 m/min in the upper 100m to ensure enough water was filtered in the shallow nets.
The MOCNESS tows were done only at the day-night stations, where one daytime and one nighttime tow were performed (cruise report, Figure 9.1.1). The definitions of day and night used for both the MOCNESS and the VPR (described below in section 9.2) were:
DAY
Start: The MOCNESS needed to be at depth ready to start sampling or the VPR starting its down-cast no earlier than 1 hour after sunrise.
End: The MOCNESS needed to be at depth starting sampling or the VPR finished its downcast sampling by 2 hours before sunset.
NIGHT
Start: The MOCNESS needed to be at depth starting its upcast sampling or the VPR starting its downcast no earlier than 1 hour after sunset.
End: The MOCNESS needed to be at the surface finished sampling or the VPR at depth finished with its downcast sampling by an hour before sunrise.
NH1208: 26 MOCNESS tows. Please see the cruise report for details.
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