14C ages of core top samples from Ontong-Java Plateau

Radiocarbon measurements on core tops from the Ontong-Java plateau confirm a previous finding by Berger and Killingley [1982] that at any given water depth, cores taken on the equator have higher accumulation rates and younger core top ages than their off-equator counterparts. Further, these new results fortify the conclusion by Broecker et al. [1991] that the increase in core top radiocarbon age with water depth rules out homogeneous dissolution within the pore waters as the dominant mechanism. Either most of the dissolution must occur prior to burial or it must occur during the first pass through the respiration-CO2-rich upper pore waters after which the calcite grains become armored against further dissolution. A puzzling aspect of this new data set is that despite the sizable difference in accumulation rate, the extent of dissolution as measured by either the CaCO3 content or the ratio of CaCO3 in the >150-µm size fraction to that in the < 63-µm fraction is no different off than on the equator. In order to reconcile the results of this study with those obtained by Hales and Emerson [1996] using in situ electrodes, it is necessary to call upon calcite armoring.

Plume-top altitude time-series during May 2011 volcanic eruption of Grímsvötn, Iceland

Plume-top altitude time series of the volcanic plume during the eruption of Grímsvötn in Iceland 21-28 May 2011. The altitude was estimated from weather radar echo top data from two weather radars, Keflavik and Klaustur. Keflavik radar is a fixed position C-band weather radar close to Keflavik International Airport, at 64°01.583'N, 22°38.150'W. The height of the antenna is 47 m a.s.l. and the distance to Grímsvötn volcano is 257 km. Klaustur radar is a mobile X-band weather radar located close to Kirkjubaejarklaustur, at 63°46.500'N, 17°57.817'W. The height of the antenna is also 47 m a.s.l. and the distance to Grímsvötn volcano is 75 km.

Texture analyses of ODP Site 131-808 sediments

The microfabric of 11 mudrock specimens from ODP Site 808 (Nankai accretionary prism) was quantitatively analyzed using X-ray texture goniometry and optical petrography. The objectives of the study were to learn about rock strain and to detect a component of bulk lateral shortening in the deformation of the mudstones. Strain evaluation is based on the predictions of March theory, and on distortions of initially homogeneous marker particle distributions (the Fry technique). The main results are as follows. The specimens underwent a strain path of progressive flattening, which is closely related to loss of pore space by vertical loading. A component of bulk lateral shortening is detectable in the top 550 mbsf at Site 808, but compared with the amount of uniaxial vertical shortening, its relative magnitude is probably small. Moreover, it cannot be said with confidence whether this is caused by toe contraction of the accretionary wedge or by gravitationally induced downslope movement of the sediment pile. The mudstones examined were deposited in a marine environment with an oxic bottom water column. Micropore collapse is an important fabric building mechanism, but below 400 mbsf its effects are at least partly overridden by recrystallization of smectite. We conclude that mud microfabrics are not very precise deformation gauges, but can be used for rough estimations of strain.

Plume-top altitude time-series during 2010 volcanic eruption of Eyjafjallajökull

The eruption of Eyjafjallajökull volcano in 2010 lasted for 39 days, 14 April-23 May. The eruption had two explosive phases separated by a phase with lava formation and reduced explosive activity. The height of the plume was monitored every 5 min with a C-band weather radar located in Keflavík International Airport, 155 km distance from the volcano. Furthermore, several web cameras were mounted with a view of the volcano, and their images saved every five seconds. Time series of the plume-top altitude were constructed from the radar observations and images from a web camera located in the village Hvolsvöllur at 34 km distance from the volcano. This paper presents the independent radar and web camera time series and performs cross validation.

Planktonic foraminiferal d18O values and apparent calcification depths of core-top samples along an east-west transect across the tropical Atlantic/Caribbean

D18O values of nine tropical-subtropical planktonic foraminiferal species with different preferential habitat depths collected from 62 core-top samples along an east-west transect across the tropical Atlantic/Caribbean were used to test the applicability of interspecific d18O gradients for reconstructions of tropical upper ocean stratification. In general, the d18O difference (Delta d18O) between intermediate- and shallow-dwelling species decreases, and Delta d18O between deep and intermediate dwellers increases with increasing thermocline depth towards the west. The statistical significance of regional differences in Delta d18O highlights Delta d18O between the intermediate dwellers (in particular Globorotalia scitula and Globorotalia tumida) and the shallow dweller Globigerinoides ruber pink, as well as Delta d18O between the deep dwellers Globorotalia crassaformis or Globorotalia truncatulinoides dextral and intermediate dwellers as most sensitive to changes in tropical Atlantic thermocline depth. Based on the observed regional variations in interspecific Delta d18O, we propose a multispecies stratification index "STRAtrop" = (d18Ointermediate - d18Oshallow) / (d18Odeep - d18Oshallow) for the tropical ocean. Statistically significant differences in STRAtrop values between the E-Atlantic and the Caribbean suggest that this index may be a useful tool to monitor variations in tropical upper ocean stratification in the geological record.