Dataset: Tioga MOCNESS logs
Deployment: TI729

The MOCNESS was equipped with nine 150-um mesh nets (nets 0-8).

TI668: The underwater unit used was #169; temperature probe was #535 and conductivity probe was #120. A connector cable converting from the 4-pin Seacon connector at the wet end of the 0.322" EM cable on the Tioga's winch to the 2-pin EO connector required by the MOCNESS was required. Both the MOCNESS and CTD required the same pins and so the dry end connectors needed to be swapped out between operations. To simplify this change over, for this cruise, Captain Ken Houtler had a new connector made for the wheelhouse, connecting the ground and first pin wires in the wheelhouse junction box to a BNC connector. The MOC or CTD deck units were then connected to this BNC. 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. 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. The 5A fuse in the underwater unit that connects to the strobe blew on the first net cast and the canister was subsequently disconnected from the system. The strobe system was removed from the MOCNESS the morning of day 2 since it was not being used.

The MOCNESS was deployed from the aft winch and A-frame. Upon recovery the nets were all hosed down with seawater and the cod-ends were sequentially removed, placed in buckets, and transferred to the forward sink and table. Net 0 was split and half was examined for Limacina retroversa, which were put in RNAlater and the remainder of the modified split was subsequently also stored in 70% ethanol. For all other nets, whole samples were preserved in 70% ethanol.

Oblique casts with the MOCNESS were made to ca. 5 m off bottom (based on the Knudsen echosounder on the ship’s depth estimate) with a ship speed nominally of 2 kts. Sampling occurred consistently for the top 5 nets which were taken at 150-100, 100-75, 75-50, 50-25, and 25-0 m. The bottom two nets were chosen adaptively to cover the lower water column and ensure that the lowest net occurred exclusively in the nephloid layer.

Cast depth has been to 10m off bottom. Typically there has been a region of fairly constant or gradually changing transmission at the bottom of the BNL, with a region of steeply changing transmission at shallower depths, ending at the top of the BNL where transmission levels off. The protocol has been to sample with net 1 from the max depth to the top of the region of constant/gradually changing transmission and then with net 2 from there to the top of the region of steeply changing transmission (ie to the top of the BNL). All samples had the ethanol replaced with fresh 70% ethanol ~24 hours after sampling.