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Paleoclimatic Variation in the Valley of Guatemala during Precolumbian Times
Appendix
The following is a detailed report provided by Dr. Brenner regarding the sampling at Lake Amatitlán.
Station 1 13 March 2000
13-III-2000-MWI. First attempt at mud-water interface (MWI) core failed, as we did not have any water on top of the interface. This try was made starting the drive 20 cm down from the top of rod #8 (i.e. 13.24 m below water surface). The retry, starting 40 cm down from the top of rod #8 yielded a good MWI core about 75 cm long. 13-III-2000-1. Nominal drive was 50-150 cm depth in the sediment, or about 25 cm overlap with the MWI core. We tried four attempts before getting a satisfactory, complete drive. 13-III-2000-2. Good, full drive (150-250 cm), though there was some bending of the rods on the way down. Will require casing pipe for further coring. Set 15 m of 3" PVC casing pipe. We repeated drive 2 and discarded the collected sediment. This was done to clean the hole to a depth of 250 cm below the sediment surface. 13-III-2000-3. Drive 3 went smoothly and we retrieved sediment from 250-350 cm. 13-III-2000-4. Drive 4 was an incomplete drive because the sediments were dense and resistant. We retrieved 67 cm of material, or 350-417 cm below the sediment/water interface. 13-III-2000-5. Drive 5 was an incomplete drive because the sediments were dense and resistant. We retrieved 58 cm of material, or 417-475 cm below the sediment/water interface. End coring.
Station 2 14 March 2000
14-III-2000-MWI. Retrieved an 80-cm MWI core with about 15 cm of water over the sediment surface. For drive 1, we marked up 65 cm on the rod from the start of the MWI drive. This accounts for 15 cm of water and 50 cm of sediment. We expect about 30 cm of overlap between drive 1 and the MWI core. 14-III-2000-1. Nominal drive was 50-150 cm depth in the sediment, but the piston did not lock and we had to push several times to complete the drive. Will set casing and redrill to 150 cm to clean out the hole. Cleaned out mud in the casing pipe to a depth 150 cm below the sediment interface. 14-III-2000-2. Good, full drive (150-250 cm). A few cm of bottom deposits were hanging from the end of the core tube on retrieval, probably due to gas expansion. Material was cut and placed in a labeled bag. There appear to be snails at some depths in this section. 14-III-2000-3. Good, full drive (250-350 cm). Took a lunch break. 14-III-2000-4. Only retrieved 75 cm (350-425 cm), and piston did not trigger properly. 14-III-2000-5. Retrieved 54 cm of mud (425-479 cm). 14-III-2000-6. Retrieved 65 cm (479-544 cm) and the sample appeared to terminate on an ash layer. We evidently hit a gas pocket because the casing had some serious bubbling going on for several minutes.
Station 3 15 March 2000
15-III-2000-MWI. Retrieved an 85 cm MWI core with about 12 cm of water over the sediment surface. We began the drive at the joint between rods #8 and #9, i.e. 13.44 m below the water surface. For drive 1, we marked up 60 cm on rod #9 from the start of the MWI drive. This accounts for 12 cm of water and ~50 cm of sediment. We expect about 35 cm of overlap between drive 1 and the MWI core. 15-III-2000-1. Nominal drive was 50-150 cm depth in the sediment. Came up full with a few cm hanging from the bottom end of the core tube. This was cut and placed in a labeled bag. 15-III-2000-2. Drive was attempted without casing. Piston did not release on first attempt. We reset piston and cored a second time without casing, retrieving a full drive (150-250 cm). Set 5 sections (15 m) of 3" PVC casing, with casing down about 1.5 m in mud. Cleaned out mud in the casing pipe to a depth 250 cm below the sediment interface. 15-III-2000-3. Good, full drive (250-350 cm). 15-III-2000-4. Complete drive (350-450 cm), but we needed to hammer through some hard material. Once we hammered through the hard section (5-10 cm thick), we pushed the rest of the drive. The second boat then pulled up to us and the turbulence moved us off station. The second boat reset one anchor and we were able to position ourselves at the casing pipe again. 15-III-2000-5. We pushed and then hammered the last ~30 cm of the drive. The nominal drive was 450-550 cm, but the section length was about 96 cm. 15-III-2000-6. Retrieved 70 cm of mud (550-620 cm), which required hammering. 15-III-2000-7. Retrieved 81 cm of mud (620-701 cm), which required hammering. There are several sand layers evident in the core.
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