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IODP Expedition 383

Dynamics of Pacific Antarctic Circumpolar Current (DYNAPACC)


Daily Science Report for 15 June 2019

Location: In transit to Site U1541 (proposed Site CSP-1A)

Science Update: Today scientists continued to discuss results from Site U1540 and to work on the site reports.

We arrived at the coordinates of Site U1541 overnight at reduced speed but continued steaming to the southwest on a 245° course to avoid a severe weather system and high seas on site. We plan to continue navigating on a weather avoidance course until midnight on 17 June, when sea/weather conditions are predicted to improve, and then turn around and return to the site.


Daily Science Report for 14 June 2019

Location: In transit to Site U1541 (proposed Site CSP-1A)

Science Update: All cores from Site U1540 have been processed and analyses of discrete samples are being finalized. Thin sections of rock fragments recovered from the bottom of Hole U1540D, in the core catcher from Core 22H, revealed highly altered volcanic glass shards, suggesting a source from the East Pacific Rise (EPR). This suggested we had recovered the complete sedimentary section at the site, from the seafloor to basement. The EPR is presently located about 200 km to the west–northwest of Site U1540, but the site’s location was very proximal to the mid-oceanic ridge ~5 Ma. Scientists met to present a summary of their results from Site U1540, and they are working on Site U1540 reports.

Today we covered 175 nmi at an average speed of 7.3 kt under high wind and sea conditions. There are 148 nmi remaining to Site U1541. The estimated time of arrival on site is still midnight on 15 June, but this could change significantly due to the weather/sea conditions encountered during the transit.


Daily Science Report for 13 June 2019

Location:
• Hole U1540E (55°8.4772′S, 114°50.5375′W; water depth 3577.2 mbsl)
• In transit to Site U1541 (proposed Site CSP-1A)

Science Update: High seas and winds engulfed our site location overnight, but conditions improved sufficiently by midafternoon to enable us to raise the thrusters and depart for Site U1541 (proposed Site CSP-1A). The vessel was underway in a westerly direction at 1600 h. The estimated time of arrival at the next site is midnight on 15 June, but this could change significantly due to the weather/sea conditions encountered during the transit.

Scientists are finalizing analyses of Site U1540 cores samples, working on reports, and preparing presentations for tomorrow’s Site U1540 science meeting.


Daily Science Report for 12 June 2019

Location: Hole U1540E (55°8.4772′S, 114°50.5375′W; water depth 3577.2 mbsl)

Science Update: Today we cored Hole U1540E from 135 to 213 mbsf (Cores 2H–10H), including a 2 m drilled interval without recovery from 144.5 to 146.5 mbsf to attain a good depth offset between cores from Holes U1540D and U1540E. Cores U1540E-2H to 10H recovered 78.9 m of sediment (104% recovery). Core U1540E-10H (203.5–213 mbsf) hit the same hard layer encountered at the bottom of Hole U1540D, and reported a partial stroke. At that point, we ended the hole and the drill crew began to recover the drill pipe. In the afternoon, the expedition management team met to discuss operational options to cope with an approaching storm at this site and also bad weather and high seas forecast at the two other primary sites in the central South Pacific over the next several days. The decision was made to ride out the weather at our current site until at least tomorrow afternoon and possibly into Friday, and then transit west to proposed Site CSP-1A, where sea conditions are expected to improve first. The drill floor was secured by 1905 h.

Cores U1540D-18H to 22X and U1540E-2H to 10H were processed, described, imaged, and X-rayed. A prominent lithologic transition from white to light gray nannofossil ooze to pale brown to brown clay and biosiliceous-bearing nannofossil ooze was observed at ~190 mbsf in both holes. Poor preservation of biogenic components suggests significant diagenetic alteration in the lowermost part of the section. Biostratigraphic and paleomagnetic analyses suggest an age of ~5 Ma at the base of Hole U1540E.

Sediment samples from Site U1540 are being analyzed for total organic carbon and total nitrogen, and interstitial water samples have been analyzed for alkalinity, pH, salinity, phosphate, silica, and ammonium. Chlorinity as well as major and minor cation and anion measurements are ongoing. Geochemical data suggest influence of hydrothermal fluid on pore water chemistry below 150 mbsf.


Daily Science Report for 11 June 2019

Location:
• Hole U1540D (55°8.4766′S, 114°50.5196′W; water depth 3577.2 mbsl)
• Hole U1540E (55°8.4772′S, 114°50.5375′W; water depth 3577.2 mbsl)

Science update: Today we completed APC coring in Hole U1540D after taking Cores 13H–23X from 131.0 to 211.0 mbsf (81.43 m of core, 102% recovery). Coring ended before reaching our target depth of 275 mbsf because Core 22H hit a hard layer at 210 mbsf, and recovered only ~0.5 m of unconsolidated sediment containing abundant gravel-size rock fragments. We then switched to the extended core barrel (XCB) coring system to try to obtain a longer core sample of the rocky material, but the attempt was unsuccessful (we advanced just 0.5 m with no recovery after 45 min of XCB coring). We pulled the drill string out of the hole, clearing the seafloor at 1710 h and ending Hole U1540D. We then moved the ship 20 m west, spaced out the drill bit, and started Hole U1540E at 1840 h. We drilled ahead without recovery to 135 mbsf by midnight.

Cores U1540D-1H to 14H (0–150 mbsf) provide a copy of the lithologic succession recovered in Holes U1540A and U1540C, enabling us to build a composite stratigraphic section at the site. The sediment in these cores consists of calcareous foraminifer and nannofossil ooze interbedded with carbonate-bearing to carbonate-rich diatom ooze. Below 150 mbsf, Cores U1540D-15H to 17H consist of white to light greenish gray, mostly homogeneous, diatom-rich to diatom-bearing nannofossil ooze interbedded with light greenish gray to greenish gray carbonate-bearing diatom ooze. Carbonate content ranges from 15 to 93 wt%, and shows a general increasing trend uphole in the upper 150 m. Biostratigraphic and paleomagnetic analyses suggest an age of 4.7 Ma at the base of Hole U1540D. Petrophysical and geochemical measurements of Hole U1540D and U1540E samples are ongoing.


Daily Science Report for 10 June 2019

Location:
• Hole U1540B (55°8.4656′S, 114°50.4985′W; water depth 3580.0 mbsl)
• Hole U1540C (55°8.4656′S, 114°50.4985′W; water depth 3580.0 mbsl)
• Hole U1540D (55°8.4766′S, 114°50.5196′W; water depth 3577.2 mbsl)

Science Update: By 0800 h, we had completed APC coring in Hole U1540B with Cores 13H to 19H penetrating from 83.5 to 150 mbsf (64.6 m recovered, 92% recovery).

We raised the drill pipe above the seafloor and repositioned the vessel 20 m south of Hole U1540B. After spacing the bit to 3587.5 mbrf we spudded Hole U1540C at 1110 h. Core 1H recovered 6.8 m of material but it lacked the characteristic light brown oxidized layer at the top of the core that would have indicated the recovery of a good sediment/water interface. Therefore, we decided to end Hole U1540C and attempt another mudline core.

We moved the vessel 20 m west of Hole U1540C and started Hole U1540D at 1235 h. Core 1H recovered 8.9 m with a noticeable light brown core top sediment layer. APC coring continued to 79.2 mbsf with three interspersed short drilled intervals to ensure an adequate core overlap for stratigraphic correlation between Holes U1540A, U1540B, and U1540C. Then, we drilled ahead without recovery to 131 mbsf. Our plan is to resume APC coring and deepen the hole to 275 mbsf.

In the afternoon we received notice that our request to extend the penetration depth from 150 to 275 mbsf at this site was approved by the IODP Environmental Protection and Safety Panel. The rationale behind our request for extending the record at Site U1540 was based on the successful recovery of a complete and continuous Pleistocene sedimentary record in Holes U1540A and U1540B. The increase in penetration depth will allow us to extend this record into the Pliocene, which is expected directly below the presently drilled maximum depth of 150 mbsf. This opportunity may allow us to recover a unique South Pacific climate legacy record covering the Pliocene Warm Period. Additional rationale was based on the current sea state. We expect another 2 d of reasonable conditions at this site allowing for further drilling, while significantly worse sea conditions are forecast at our two other primary sites in the South Pacific.

Physical properties measurements have been completed for Holes U1540B and U1540C and are ongoing for Hole U1540D. Cores U1540A-13H to 16H were split, described, scanned for color reflectance, and X-rayed. Sediment in this lower part of the cored section is dominated by carbonate-rich diatom ooze and diatom-rich to diatom-bearing nannofossil ooze. Each of the cores covers about two cycles of these gradual lithologic changes. Cores U1540B-1H to 19H also were split and described. They provide a duplicate of the lithological Pleistocene record recovered at the site. GRA density, P-wave, and magnetic susceptibility measurements show distinct variations associated with lithologic changes. Geochemical analyses of sediment and interstitial water samples are in progress.


Daily Science Report for 9 June 2019

Location:
• Hole U1540A (55°8.4674′S, 114°50.5188′W; water depth 3589.7 mbsl)
• Hole U1540B (55°8.4656′S, 114°50.4985′W; water depth 3580.0 mbsl)

Science Update: Today we deepened Hole U1540A from 102.8 mbsf to a total depth of 150 mbsf (Cores 12H–16H; 49.5 m recovered, 105%). After recovering the last core, the bit was pulled back to 3561 mbrf, clearing the seafloor at 0900 h and ending Hole U1540A. APCT-3 formation temperature measurements were taken on Cores U1540A-4H, 7H, 10H, 13H, and 16H. A misfire was recorded on Core 16H.

The vessel was moved 20 m east of Hole U1540A in preparation to start Hole U1540B. Having determined that Core 1H in Hole U1540A was taken from below the seafloor, the drill bit was raised to 3575 mbrf (20 m higher than in Hole U1540A) to take the first core. The first attempt at Core U1540B-1H returned an empty liner. The drill bit was repositioned to 3584.5 mbrf (9.5 m lower), and Hole U1540B was spudded at 1220 h with Core 1H recovering 3.12 m of sediment. This determined a seafloor depth of 3590.9 mbsl. APC coring continued to 83.5 mbsf (Cores 2H through 12H) with two short drilled intervals (total of 10 m) to ensure a good offset between cores from Holes U1540A and U1540B. Total core recovery from Hole U1540B was 76.2 m (96%) by the end of the day.

Cores U1540A-5H through 16H have been measured for paleomagnetic and physical properties, split, X-rayed, and described. The sediment consists of predominantly calcareous foraminifer and nannofossil ooze interbedded with carbonate-bearing to carbonate-rich diatom ooze. An obvious lithologic change to even more carbonate-dominated facies is observed around 70 mbsf, and is supported by a marked shift in physical properties values (e.g., higher density). The bottom of Hole U1540A (150 mbsf) is estimated to be ~2.5 Ma based on biostratigraphic and paleomagnetic data. Scientists are finishing their reports from Site U1539, and analyses of samples from Hole U1540A are ongoing.


Daily Science Report for 8 June 2019

Location: Hole U1540A (55°8.4674′S, 114°50.5188′W; water depth 3589.7 mbsl)

Science Update: Drill floor operations resumed at 0415 h after sea conditions improved sufficiently to continue to deploy the drill pipe. The end of the pipe was lowered from 2171 to 3595 mbrf and the bit was spaced out in preparation to start Hole U1540A. At 0905 h, Core U1540A-1H penetrated from the seafloor to 9 mbsf, recovering 8.93 m of sediment. APC coring continued for the rest of the day, with Cores 2H–11H deepening the hole to 102.8 mbsf. Total recovery for the day was 105.6 m (103%).

Cores U1540A-1H through 4H were measured for physical properties, split, X-rayed, and described. The sediment consists of predominantly whitish to light gray strongly bioturbated carbonate-rich oozes interbedded with greenish gray diatom ooze. Comparison between the Cores 1H and 2H physical properties data and those from a gravity core collected near our location during the site survey cruise suggested that the uppermost ~200,000 y of the record are missing from the top of Hole U1540A. This was confirmed by the biostratigraphers, which led us to determine that Core 1H did not recover the sediment-water interface; likely, it was taken from below the seafloor. We will attempt to recover this interval in the next hole. Scientists finished most remaining Site U1539 analyses, met to present a summary of their results, and are working on their site reports.


Daily Science Report for 7 June 2019

Location:
• Transit to Site U1540 (proposed Site CSP-7A)
• Hole U1540A (55°8.4666′S, 114°50.5182′W; water depth 3589.7 mbsl)

Science Update: After recovering the drill string, the rig floor was secured for transit at 0130 h. We raised the thrusters and began the sea voyage to Site U1540 (proposed Site CSP-7A) at 0230 h. After a 61 nmi transit at an average speed of 10 kt, we arrived at Site U1540 at 0907 h, switched to dynamic positioning, and began rigging operations. We built the APC/XCB bottom-hole assembly and started to lower the drill string to the seafloor as the seas were picking up. Sea conditions continued to deteriorate throughout the day, and at 1645 h, with a ship heave of >6 m and the drill bit at 2171 mbrf (2160 mbsl), the decision was made to pause drill floor operations and wait for the seas to come down before continuing to lower the pipe. The maximum heave experienced today was 7.4–7.6 m between 1700 h and 1900 h.

All cores from Hole U1539D have been measured for physical and paleomagnetic properties, imaged, and described lithologically. Cores U1539D-13H through 21H consist of alternating biosiliceous and calcareous oozes. Biosiliceous lithologies are dominant in the sedimentary sequence. At 1145 h, the Co-Chief Scientists presented the scientific and operational objectives for Site U1540. Scientists are working on Site U1539 reports and preparing presentations for tomorrow’s site summary meeting.


Daily Science Report for 6 June 2019

Location: Hole U1539D (56°9.072′S, 115°8.047′W; water depth 4070.2 mbsl)

Science Update: APC coring continued in Hole U1539D, deepening the hole from 93 mbsf to a final depth of 198 mbsf by 1500 h. Cores U1539D-8H to 21H recovered 94.9 m (93%). Core 17H registered a partial stroke, but was retrieved full. The rest of the day was spent recovering the drill pipe and preparing for departure to Site U1540 (proposed Site CSP-7A). In total, 61 cores were taken at Site U1539 and 502.3 m (94.2%) of core was recovered.

Cores U1539C-27F through 32F consist of greenish gray to light gray carbonate-bearing and carbonate-rich diatom ooze. Pervasive drilling disturbance was observed in the first section of Cores 27F, 28F, 29F, and 32F. All cores from Hole U1539D have been measured for physical properties, and Cores U1539D-2H through 12H have been described. They consist predominantly of carbonate-rich diatom ooze. Drilling disturbance is observed in most cores and varies from slight to high.

Fifty-two samples from Site U1539 have been analyzed for calcium carbonate. While sediment at this site is rich in biogenic silica, CaCO3 contents as high as >90 wt% were measured between 70 and 75 mbsf in Hole U1539A. Total carbon and nitrogen samples are currently being prepared for analyses. Phosphate, ammonium, and major ion analyses using ICP-AES on interstitial water samples have been completed, and sample preparation for dissolved silica is currently underway.

A live broadcast was held with The School at Columbia University in New York.


Daily Science Report for 5 June 2019

Location:
• Hole U1539C (56°9.071′S, 115°8.028′W; water depth 4071.2 mbsl)
• Hole U1539D (56°9.072′S, 115°8.047′W; water depth 4070.2 mbsl)

Science Update: Weather and sea conditions remained fair throughout the day and into the night, allowing us to deepen Hole U1539C from 224.7 (Core 25H) to 268.1 mbsf (Core 32F), with a core recovery of 84%. Cores 25H to 27H registered partial strokes and experienced overpull upon retrieval. Therefore, we switched to the half-length APC (HLAPC) coring system on Core 28F to improve core quality. Given the relatively better than expected sea and weather conditions, and the slower core recovery with the HLAPC system, we decided to end Hole U1539C at 1230 h and start a new hole with the objective of duplicating the lower stratigraphic section not recovered in Hole U1539A so that we can build a composite section for most of the sedimentary succession recovered at the site.

The drill string was pulled up above the seafloor and prepared for starting Hole U1539D. At 1400 h, with the vessel offset 20 m west of Hole U1539C, we started Hole U1539D by drilling ahead without recovery to 47 mbsf, where we paused to spot core a short interval that was not recovered in Hole U1539C. Cores U1539D-2H and 3H (47.5–62.8 mbsf, 101%) filled the gap, and from that point down to 93 mbsf (Core 7H) we alternated short drilled and cored intervals to ensure an offset between cores from Holes U1539A, U1539C, and U1539D. The core recovered from Hole U1539D was 33.32 m (73%) by the end of the day.

All cores from Hole U1539C have been measured for physical properties and most have been described lithologically. Cores U1539C-14H through 26H consist of alternating biosiliceous and calcareous oozes. Biosiliceous lithologies are dominant in the sedimentary sequence and include greenish gray to light gray carbonate-bearing and carbonate-rich diatom ooze, whereas carbonate lithologies include diatom-rich nannofossil ooze and diatom-bearing calcareous ooze. A thick ~5 m bed of homogenous diatom-rich calcareous ooze with an erosive lower contact, normal grading, and cross-laminae interrupts the stratigraphic sequence in Cores U1539C-18H and 19H. Dropstones have been counted in all Hole U1539A X-ray images. A greater abundance of dropstones observed in diatom ooze lithofacies is associated with glacial periods.

Interstitial water samples from Hole U1539C have been measured for alkalinity, and measurements of major elements and chlorinity are in progress. Analyses of carbonate and organic matter content of sediment samples are also ongoing.


Daily Science Report for 4 June 2019

Location: Hole U1539C (56°9.071′S, 115°8.028′W; water depth 4071.2 mbsl)

Science Update: Today we continued to deepen Hole U1539C. Cores 8H to 24H penetrated from 66.5 to 224.7 mbsf and recovered 153.23 m (97%). Cores 17H to 24H experienced more than 50 klb of overpull upon retrieval. The Core 22H liner shattered spirally over a ~1.5 m section and had to be pumped out of the barrel, and a partial stroke was reported for Core 24H. Successful formation temperature measurements were taken on Cores U1539C-13H (124.15 mbsf) and 16H (152 mbsf). Aware of the deteriorating weather conditions forecasted for our current location, and over all our other primary and alternate sites in the central South Pacific, the expedition management team and the ship’s crew met to discuss options for our operations plan. Rough weather and high seas are predicted to settle overnight and continue over the next several days. Therefore, we decided to take advantage of the current favorable conditions to deepen Hole U1539C as much as we can before high heave and roll prevent us from coring anymore. At this time, the plan is to terminate the hole and pause operations until weather/sea conditions improve sufficiently to either start a new hole at Site U1539 or go to another site.

Cores U1539C-4H through 13H were measured for physical and paleomagnetic properties. The cores consist of alternating biosiliceous and calcareous oozes. Biosiliceous lithologies are dominant in the sedimentary sequence and include greenish gray to light gray carbonate-bearing and carbonate-rich diatom ooze, whereas carbonate lithologies include diatom-rich nannofossil ooze and diatom-bearing calcareous ooze. Bioturbation is moderate to high and diatom mats are extensive in Core 13H. The age at the base of Core 18H is estimated at >1.24 Ma based on calcareous nannofossil and diatom biostratigraphy.

Carbonate content has been measured in discrete samples down to 88 mbsf in Hole U1539A. Total organic carbon analyses have also been completed for the upper 50 m in Hole U1539A. Twenty-eight whole-round samples from Hole U1539C have been processed for routine shipboard analyses of interstitial water.


Daily Science Report for 3 June 2019

Location:
• Hole U1539B (56°9.059′S, 115°8.027′W; water depth 4070.5 mbsl)
• Hole U1539C (56°9.071′S, 115°8.028′W; water depth 4071.2 mbsl)

Science Update: Coring operations resumed at 0330 h, after weather and sea conditions improved overnight. The drill bit was lowered from 4030 mbrf (to where it had been raised the day before while waiting on weather) to 4081 mbrf (or ~1 m above the seafloor) to start Hole U1539B. Hole U1539B was spudded at 0540 h with Core U1539B-1H recovering 9.21 m (100%); this determined the seafloor depth at 4070.5 mbsl. APC coring continued to 28.2 mbsf with Cores 2H and 3H recovering 5.92 m (62%) and 6.79 m (71%), respectively. The shear pins sheared prematurely on all cores, indicating that the ship’s heave (≥4 m) was still too high to obtain good quality cores. Therefore, we decided to end the hole and wait until the ship’s heave dropped to <3 m before we started coring again in a new hole. The drill string was pulled out of the hole, and the bit was raised to 4060 mbrf at 1015 h.

At 1300 h, we lowered the bit to the seafloor and installed the sinker bars and the orientation tool in preparation for starting Hole U1539C. Core U1539C-1H was taken at 1415 h, recovering 9.7 m (102%); this determined the seafloor depth at 4071.2 mbsl. We continued APC coring, deepening Hole U1539C to 66.5 mbsf by midnight (Cores 2H to 7H). The average core recovery for this interval was 83% as a result of recovering only 0.27 m (3%) in Core 6H, which is believed to have encountered a large dropstone based on damage visible on the APC cutting shoe.

Cores U1539B-1H through 3H and U1539C-1H and 3H consist of alternating light greenish gray to dark gray carbonate-bearing diatom ooze with thinner beds of diatom-rich nannofossil ooze. A pale brown diatom rich nannofossil ooze characterizes the uppermost ~50 cm of each hole. Bioturbation is moderate to high. The age at the base (107 mbsf) of the sedimentary succession recovered in Hole U1539A is ~600 ka. Interstitial water samples from Hole U1539A have been measured for salinity, alkalinity, pH, phosphate, ammonia, and major and trace elements.


Daily Science Report for 2 June 2019

Location: Hole U1539A (56°9.06′S, 115°8.0461′W; water depth 4071.1 mbsl)

Science Update: After repairing a leak in the aft core winch line load cell, coring continued in Hole U1539A, recovering Cores 11H (78%) and 12H (100%) from 90.1 to 107.6 mbsf. The Core 11H liner shattered, and the shear pins sheared prematurely on both cores. With the sea state rapidly deteriorating and core quality questionable, we decided to terminate coring in Hole U1539A after Core 12H. The drill string was pulled back out of the hole and raised to ~200 m above the seafloor. Winds remained high throughout the day, fluctuating between 30 and 40 kt, and wave height ranged from 4 to >6 m. The rest of the day was spent waiting on the weather to improve.

Cores U1539A-4H through 10H are dominated by light greenish gray to dark gray carbonate-bearing diatom ooze with thinner beds of diatom-rich nannofossil ooze. Dropstones >2 mm and diatom mats are primarily observed in diatom ooze intervals. A prominent >2 m thick interval of white diatom-bearing nannofossil ooze characterizes the upper portion of Core 9H. Lithologic changes correlate well with physical properties changes, which follow glacial/interglacial cycles. Biosiliceous and calcareous biostratigraphic markers indicate an age of ~600 ka at the base of Core 12H.


Daily Science Report for 1 June 2019

Location: Hole U1539A (56°9.06′S, 115°8.0461′W; water depth 4071.1 mbsl)

Science Update: The day started while preparing the coring tools and lowering the drill string to the seafloor. At 0450 h, after servicing the rig and installing the sinker bars and the core orientation tool, the drill bit was positioned at 4077 mbsl—5 m above the seafloor depth (4082.4 m) based on the position depth recorder (PDR)—in preparation for taking the first core of the expedition. Coring in Hole U1539A started at 0525 h with Core U1539A-1H recovering 4.56 m (99%) and establishing a seafloor depth of 4071.1 m. Continuous APC coring continued until retrieving Core U1539A-10H from 90.1 mbsf at 1900 h. At that point we stopped coring operations to repair the aft core winch load cell. Coring resumed at 2245 h and one more core (U1539A-11H) was taken before midnight from 90.1 to 99.6 mbsf, recovering 7.4 m (78%), with weather and sea conditions quickly deteriorating.

In the laboratories, Cores U1539-1H through 10H were measured for physical properties in the Whole Round Multisensor Logger (WRMSL). Gamma ray attenuation (GRA) density measurements usually were not reliable on the first section of a core due to the presence of water inside the liner in the uppermost meter of every core. Physical properties measurements on Core U1539A-5H also were compromised because the core liner shattered upon retrieval, and the core and the liner had to be restored in the core receiving platform. Thermal conductivity was measured once per core in Cores U1539A-2H through 6H.

Cores U1539A-1H through 3H were split, imaged, and described. They consist of alternations between nannofossil-rich diatom ooze and diatom-rich nannofossil ooze. The age at the base of Core U1539A-10H is estimated at >0.44 Ma based on siliceous and calcareous biostratigraphic markers. In the Geochemistry Laboratory, interstitial water from 30 whole-round samples is being measured for alkalinity, pH, and chlorinity. Headspace samples were taken from every core to monitor hydrocarbon gases. Methane concentrations are within 17 ppmv.