Sedimentological investigations

The sampled sites are shown on figures 5, 6 and 7. As mentioned in the operational report, some sampling sites were cancelled or the coring failed. Here, only the successful Hamon grab samples are shown. This campaign probably was the first time this tool was used in deep-water environments (Fig. 19). A comparison between the water depth on multibeam or sonar and the length of the cable when the grab hits the sea floor yields a minimal difference, suggesting the grab is heavy enough to descend straight to the sea floor and is not deviated by currents. Only the trigger of the grab is a sensitive point and was adapted to respond very quickly. For all safety, approximately 20 m cable extra was added after the seafloor was reached. After recovery, the bulk sample was photographed and described, respectively followed by sampling for microbiology, sedimentology and biology. A recapitulative list of grabs is given in table 2.

Figure 19: Hamon grab operations on board R/V Belgica.

Core number Latitude Longitude Water Depth

Recovery length/width

Remarks

B05-1201-hg 35°26.029’N 6°46.877’W 499 m 47 / 30 cm Top mud volcano B05-1208-hg 35°18.922’N 6°48.056’W 550 m 40 / 24 cm Top mound PDE B05-1209-hg 35°18.686’N 6°47.917’W 546 m 28 /23 cm Top mound PDE B05-1211-hg 35°17.660’N 6°47.200’W 550 m 40 / 20 cm MOMA-02A

B05-1212-hg 35°17.528’N 6°47.150’W 550 m 40 /20 cm Between MOMA-01A and MOMA-02A B05-1214-hg 35°13.859’N 6°33.456’W 280 m 35 / 21 cm East of Al Idrisi B05-1215-hg 35°14.500’N 6°33.378’W 302 m 44 / 22 cm East of Al Idrisi B05-1216-hg 35°17.702’N 6°39.182’W 414 m Low recovery Flank of Al Idrisi (seep

site) Table 2: List of obtained Hamon grabs and relevant data

4.5.1 B05-1201-hg (499 m bsl)

This first grab was taken on the top of a supposed mud volcano at the northwestern edge of the Vernadsky Ridge. The sediment is a brownish sandy, soupy clay with clasts (siltstone), a few coral fragments and biogenic fragment, scaphopods,…). Downwards, a transition towards greyish sandy to silty, compacter clays is visible.

Sedimentological subsamples consist of 1 bag with bulk sediment and 1 bag with clasts. For microbiology, 3 times 1.5 ml sample was fixed in 4% paraformaldehyde PBS, then washed in ethanol PBS and stored at -20°C. 1 45 ml sample was stored directly at -20°C. No live or washed out biological samples were taken.

Hamon grab sample B05-1201-hg: Washed out clasts from mud volcano

4.5.2 B05-1208-hg (550 m bsl)

This sample was taken on the top of a mound on Pen Duick escarpment. The sediment is a brownish sandy to silty clay with a lot of coral fragments (abundant Desmophyllum fragments) and small biogenic fragments (spikes of echinoderms, gastropods, sponge spiculae,…).

Sedimentological subsamples consist of 1 bag with bulk sediment from the top layer and 1 bag of bulk sediment from the bottom layer. For microbiology, 3 times 1.5 ml sample was fixed in 4% paraformaldehyde PBS, then washed in ethanol PBS and stored at -20°C. 1 45 ml sample was stored directly at -20°C. 2 bagged boxes with

washed out biological samples were taken, but no live biological samples.

4.5.3 B05-1209-hg (546 m bsl)

This sample was also taken on the top of a mound on Pen Duick escarpment. The upper 10 cm are dominated by brownish sandy clays with dead, partly oxidized coral fragments (Lophelia pertusa, Madrepora oculata) and smaller biogenic fragments (bivalve fragments, sponge spiculae, sea urchin needles). Transition to greyish, compact silty clay at 7 cm depth.

Sedimentological subsamples consist of 1 bag with bulk sediment from the top layer and 1 bag of bulk sediment from the bottom layer. For microbiology, 3 times 1.5 ml sample was fixed in 4% paraformaldehyde PBS, then washed in ethanol PBS and stored at -20°C. 1 45 ml sample was stored directly at -20°C. 7 bagged boxes with washed out biological samples were taken, and 1 bucket with live biological samples, the latter fixed in 8% formaldehyde.

4.5.4 B05-1211-hg (550 m bsl)

This sample was targeted at the proposed IODP site MOMA-02A. The upper 2 cm consist of soupy, brownish, sandy clay with dead coral fragments going over in greyish sandy clays with dead coral and biogenic fragments.

Sedimentological subsamples consist of 1 bag with bulk sediment from the top layer, 1 bag of bulk sediment from the bottom layer and 1 small bag with washed clasts. For microbiology, 3 times 1.5 ml sample was fixed in 4% paraformaldehyde PBS, then washed in ethanol PBS and stored at -20°C. 1 45 ml sample was stored directly at -20°C. 6 bagged boxes with washed out biological samples were taken, and 1 bucket with live biological samples, the latter fixed in 8% formaldehyde.

4.5.5 B05-1212-hg (550 m bsl)

This sample was taken between sites MOMA-01A and 02A on Pen Duick escarpment.

Brownish, sandy clays are found over the entire length of the grab with a high amount of dead coral fragments (large solitary fragments of Desmophyllum up to a length of 7 cm) and biogenic fragments. Live soft corals were observed on the surface. Small oxidized nodules were present between the sandy clays.

Sedimentological subsamples consist of 1 bag with bulk sediment from the top layer and 1 bag of bulk sediment from the bottom layer. For microbiology, 3 times 1.5 ml sample was fixed in 4% paraformaldehyde PBS, then washed in ethanol PBS and stored at -20°C. 1 45 ml sample was stored directly at -20°C. 6 bagged boxes with washed out biological samples were taken, and 1 bucket with live biological samples, the latter fixed in 8% formaldehyde.

4.5.6 B05-1214-hg (280 m bsl)

This sample is located east of Al Idrisi mud volcano, on small, mound-like features observed on CADIPOR 2 multibeam imagery.

The upper 5 cm contain brownish, oxidized silty clays (finer material than observed in the other grabs) with a lot of dead coral fragments (mainly Lophelia pertusa and Madrepora occulata).

Underneath this interval, greyish, silty, stiff clays are present with small coral fragments.

Sedimentological subsamples consist of 1 bag with bulk sediment from the top layer and 1 bag of bulk sediment from the bottom layer. For microbiology, 3 times 1.5 ml sample was fixed in 4% paraformaldehyde PBS, then washed in ethanol PBS and stored at -20°C. 1 45 ml sample was stored directly at -20°C. 6 bagged boxes with washed out biological samples were taken, and 1 bucket with live biological samples, the latter fixed in 8% formaldehyde.

Hamon grab sample B05-1214-hg: dead coral fragment (Madrepora occulata)

4.5.7 B05-1215-hg (302 m bsl)

As B05-1214-hg, this sample is located as well east of Al Idrisi mud volcano. The upper 4 cm contain brownish silty, soupy clay with a lot of dead coral fragments and other biogenic fragments (bivalves, gastropods, echinoderm fragments,…). Below, a greyish compact, silty clay is found with small coral fragments.

Sedimentological subsamples consist of 1 bag with bulk sediment from the top layer and 1 bag of bulk sediment from the bottom layer.

For microbiology, 3 times 1.5 ml sample was fixed in 4% paraformaldehyde PBS, then washed in ethanol PBS and stored at -20°C. 1 45 ml sample was stored directly at -20°C. 6 bagged boxes with washed out biological samples were taken, but no live biological samples.

4.5.8 B05-1216-hg (414 m bsl)

This last grab sample was targeted at the flank of Al Idrisi mud volcano, at the location of a supposed seepage site, as suggested by video imagery. The recovery was rather low and yielded very soupy brownish silt with some bivalve fragments.

Sedimentological subsamples only consist of 1 bag with bulk sediment from the top layer. For microbiology, 3 times 1.5 ml sample was fixed in 4% paraformaldehyde PBS, then washed in ethanol PBS and stored at -20°C. 1 45 ml sample was stored directly at -20°C. No live or washed out biological samples were taken.