Wecoma daily report, 20 August 2001

At 0130 on Monday (8/20) morning we deployed SeaSoar at 8E to start Bigbox 4sampling from south to north. We have finished line 8 at 43 45'N and observed two southward jets: an inshore upwelling jet centered at 124.4W with 30+ cm/s currents and a jet coming off Heceta Bank centered at 124.85 with 50+ cm/s speed. Elevated surface chl is seen on the inshore sides of both these jets. The high chl water is still streaming off the southern end of the Bank. Subsurface temperature variability (inversions at ~50-100m) is still high. Surface temperatures offshore are up to 16.6 C and the tuna fleet is thick near 8W. Winds came up to 20 knots from the north over the last day, but are now down to around 15 knots.

Since the last report, we completed two more circuits of our Smallbox South region, doing laps around the E-W sampling Thompson. We completed a second set of MOCNESS and vertical zooplankton net stations going from on the Bank to off along the 124.7W line. A copy of Jesse Lamb's report from the first set of stations is attached below. We moved the stations slightly onshore from our first set in order to be in the center of the high-chl water leaving the Bank. We completed stations in the Heceta Bank Overflow (HBO) region at 43 58'N (HBO5, 130m), 43 54'N (HBO6, 225m), 43 51'N (HBO7, 330m) and 43 48'N (HBO8, 440m). We observed high chl at the surface at all stations. A subsurface low-light transmission layer was observed at HBO5 (30 mab==meters above bottom), HBO6 (60 mab), HBO7 (150-225m and 30 mab) and HBO8 (20 mab only). We think the low-light transmission layer at the station seaward of the shelfbreak (HBO7) contains material advected off the Bank. This could be related to the phytoplankton detritus that Jesse mentions in his report for the offbank station of the night before. It will be interesting to see what the Thompson measurements show along their southernmost E-W line along 43 51.5'N.

We plan to complete Bigbox 4 in the early AM on Wednesday. We then have twodays to do some more Smallbox and station work before spending our final twodays (Fri-Sat) sampling the Bigbox grid. For the final Bigbox grid we will mount ISUS, the optical nitrate sensor, on SeaSoar. It will be useful to make some passes near Thompson as Burke's system pumps and measures subsurface nutrient levels so that we may compare the direct and optically measured nitrate values. We'll coordinate that with the Thompson scientists.

Submitted at 1130 on 20 August 2001 by Jack Barth, Chief Scientist,
R/V Wecoma

Heceta Bank Overflow Zooplankton Collection Results, 18-Aug-01 (PST)
Jesse Lamb

Three stations were sampled with the 1m-MOCNESS net. These stations were done in an order of south to north, with an emphasis on nighttime sampling. We started with a station south of Heceta Bank (HBO1), moving to a station located on the slope of Heceta Bank (HBO 3), then finally moving to a station located on the Bank itself (HBO 4). Other stations sampled were omitted due to the need for nighttime sampling.

HBO1 was the first station sampled. The location of this station was 43 48'N, 124 48'W. This station was located 6nm south of Heceta bank, with a depth of around 500m. Our nets sampled only to 350m starting around 23:40 (PST). At the lower depths (350 - 200m), we found primarily gelatinous plankton in the form of siphonophores, pleurobranchia, and large chaetognaths; with small numbers of euphausids, small copepods, amphipods, shrimp, cteropods, and myctophid fish. Within more of the middle layers (200 - 60m), we found more in the form of euphausids, small copepods, sergestid shrimps, than in the bottom layers, but never in any great numbers. These were mixed with the aforementioned gelatinous species. In the layer between the surface and 60 m, we found more variety of gelatinous plankton in the form of praya siphonophores, dolioids, corolla, pleurobranchia, chaetognaths, and many salps on the surface. Intermixed with these gelatinous creatures were around twenty euphausids, some amphipods and cteropods ( probably Limacina sp.).

It must be said that intermixed in most of these nets was a type of unknown phytoplankton. Because it was found at deeper depths, it could be a form of detritus, but this is unknown.

HBO3 was the next station; being sampled at 03:09 (PST). The station location was 43 53'.29N, 124 48'.07W. This station was located at a depth of 180m, right on the slope of Heceta bank. While sampling, the ship started drifting north, before following the 170m isobath. At this station we sampled from 160m up, finding large numbers of adult euphausids and large copepods, primarily. We found a mean of about 2000 euphausids per net, excluding net 5, where we found only around 300. Both euphausid species Euphausia pacifica and Thysanoessa spinifera were seen. Along with these species a large copepod, Neocalanus sp., was found in very large numbers (108 at largest). Scattered within this animals were few gelatinous species (pleurobranchia and cheatognaths), amphipods and other smaller copepods.

The last station, HBO4, had a sampling starting time of 05:05 (PST). This station location was 43 58'N, 124 48'W. The station depth was around 125m, located right on Heceta bank. Our depth was pretty uniform here, and we sampled to a depth of 115m. It must be said here that noting a reading of the HTI, that our net-0 on the MOCNESS, which is our initial downcast, went through a very dense patch that seemed to encompass the entire water column. This net had around 5000 euphausids, very many copepods of all sizes, about 100 pleurobranchia, few shrimp and amphipods. Our other nets, which sample specific layers, sampled just out of this patch. From the bottom to about 50 meters, we found smaller numbers of copepods of all sizes, around 200 amphipods, and a few chaetognaths. >From 50 - 20m we found many very small copepods, fifty amphipods, ten euphausids, five pleurobranchia, and one crab megalope. From 20m to the surface we found the same large numbers of small copepods, with smaller numbers of amphipods (around twenty). There was and increase of pleurobranchia, going from five in the 50-20m layer, to around one hundred at the surface net.