Global compilation of benthic data sets I

Approaches to quantify the organic carbon accumulation on a global scale generally do not consider the small-scale variability of sedimentary and oceanographic boundary conditions along continental margins. In this study, we present a new approach to regionalize the total organic carbon (TOC) content in surface sediments (<5 cm sediment depth). It is based on a compilation of more than 5500 single measurements from various sources. Global TOC distribution was determined by the application of a combined qualitative and quantitative-geostatistical method. Overall, 33 benthic TOC-based provinces were defined and used to process the global distribution pattern of the TOC content in surface sediments in a 1°x1° grid resolution. Regional dependencies of data points within each single province are expressed by modeled semi-variograms. Measured and estimated TOC values show good correlation, emphasizing the reasonable applicability of the method. The accumulation of organic carbon in marine surface sediments is a key parameter in the control of mineralization processes and the material exchange between the sediment and the ocean water. Our approach will help to improve global budgets of nutrient and carbon cycles.

(Table 1) Relative abundance of planktonic foraminifers in ODP Hole 164-997A sediments

Hole 997A was drilled during Leg 164 of the Ocean Drilling Program at a depth of 2770 m on the topographic crest of the Blake Ridge in the western Atlantic Ocean. We report here an analysis of the faunal assemblages of planktonic foraminifers in a total of 91 samples (0.39-91.89 mbsf interval) spanning the last 2.15 m.y., latest Pliocene to Holocene. The abundant species, Globigerinoides ruber, Globigerinoides sacculifer, Neogloboquadrina dutertrei, Globorotalia inflata, and Globigerinita glutinata together exceed over ~70% of the total fauna. Each species exhibits fluctuations with amplitudes of 10%-20% or more. Despite their generally low abundance, the distinct presence/absence behavior of the Globorotalia menardii group is almost synchronous with glacial-interglacial climate cycles during the upper part of Brunhes Chron. The quantitative study and factor analysis of planktonic foraminiferal assemblages shows that the planktonic foraminiferal fauna in Hole 997A consists of four groups: warm water, subtropical gyre (mixed-layer species), gyre margin (thermocline/upwelling species), and subpolar assemblages. The subtropical gyre assemblage dominates throughout the studied section, whereas the abundance of gyre margin taxa strongly control the overall variability in faunal abundance at Site 997. In sediments older than the Olduvai Subchron, the planktonic foraminiferal faunas are characterized by fluctuations in both the subtropical gyre and gyre margin assemblages, similar to those in the Brunhes Chron. The upwelling/gyre margin fauna increased in abundance just before the Jaramillo Subchron and was dominant between 0.7 and 1.07 Ma. The transition from this gyre margin-dominated assemblage to an increase in abundance of the subtropical gyre and gyre margin species occurred around 0.7 Ma, near the Brunhes/Matuyama boundary. The presence of low-oxygen-tolerant benthic foraminifers, pyrite tubes, and abundant diatoms below the Brunhes/Matuyama boundary suggests decreased oxygenation of intermediate waters and more upwelling over the Blake-Bahama Outer Ridge, perhaps because of weaker Upper North Atlantic Deep Water ventilation. The changes in the relative composition of foraminifer assemblages took place at least twice, around 700 and 1000 ka, close to the ~930-ka switch from obliquity-forced climate variation to the 100-k.y. eccentricity cycle. The climate shift at 700 ka suggests a transition from relatively warmer conditions in the early Pleistocene to warm-cool oscillations in the Brunhes Chron.

Secchi depth maps for the Baltic Sea, 2003-2012, with links to GeoTIFs

Secchi depth is a measure of water transparency. In the Baltic Sea region, Secchi depth maps are used to assess eutrophication and as input for habitat models. Due to their spatial and temporal coverage, satellite data would be the most suitable data source for such maps. But the Baltic Sea's optical properties are so different from the open ocean that globally calibrated standard models suffer from large errors. Regional predictive models that take the Baltic Sea's special optical properties into account are thus needed. This paper tests how accurately generalized linear models (GLMs) and generalized additive models (GAMs) with MODIS/Aqua and auxiliary data as inputs can predict Secchi depth at a regional scale. It uses cross-validation to test the prediction accuracy of hundreds of GAMs and GLMs with up to 5 input variables. A GAM with 3 input variables (chlorophyll a, remote sensing reflectance at 678 nm, and long-term mean salinity) made the most accurate predictions. Tested against field observations not used for model selection and calibration, the best model's mean absolute error (MAE) for daily predictions was 1.07 m (22%), more than 50% lower than for other publicly available Baltic Sea Secchi depth maps. The MAE for predicting monthly averages was 0.86 m (15%). Thus, the proposed model selection process was able to find a regional model with good prediction accuracy. It could be useful to find predictive models for environmental variables other than Secchi depth, using data from other satellite sensors, and for other regions where non-standard remote sensing models are needed for prediction and mapping. Annual and monthly mean Secchi depth maps for 2003-2012 come with this paper as Supplementary materials.

Quaternary carbonate record of ODP Hole 115-709A

The CaCO3 content in Quaternary deep-sea sediments from Pacific and Atlantic oceans have been suggested to respond differently to glacial/interglacial cycles; CaCO3 contents are highest during glacials in the Pacific but highest during interglacials in the Atlantic Ocean. It is not yet clear as to whether a Pacific or an Atlantic pattern of CaCO3 fluctuations dominates the Indian Ocean. We have analyzed the Ocean Drilling Program (ODP) Site 709A from the western equatorial Indian Ocean for the last 1370 ka to determine the relationships between percentages and fluxes of CaCO3 and Quaternary paleoclimatic changes. We also analyzed the coarse (>25 µm) and fine (<25 µm) fractions of CaCO3 in an attempt at estimating the influence of differences in productivity of foraminifera and calcareous nannofossils in shaping the CaCO3 record. Carbon isotopes and Ba/Al ratios were used as indices of productivity. Percentages and fluxes of CaCO3 in the total sediment and <25 µm fraction do not show any clear relationships to glacial/interglacial cycles derived from d18O of the planktonic foraminifera Globigerinoides ruber. This indicates that CaCO3 fluctuations at this site do not show either a Pacific or an Atlantic pattern of CaCO3 fluctuations. Fluxes of CaCO3 (0.38 to 2.46 g/cm**2/ ka) in total sediment and Ba/Al ratios (0.58 to 3.93 g/cm**2/ka) show six-fold variability through the last 1370 ka, which points out that productivity changes are significant at this site. Fluxes of the fine CaCO3 component demonstrate a 26-fold change (0.02 to 0.52 g/cm**2/ka), whereas the coarse CaCO3 component exhibit eight-fold change (0.13 to 1.07 g/cm**2/ka). This suggests that productivity variations of calcareous nannofossils are greater in comparison with the foraminifera. On the other hand, mean values of coarse CaCO3 fluxes are higher compared to those of fine CaCO3, which reveals that the foraminifera contribute more to the bulk CaCO3 flux than the calcareous nannofossils in the equatorial Indian Ocean.

XRF iron (Fe) counts of ODP Hole 171-1050A and 171-1051A

Upper Paleocene to lower Eocene sediments drilled at Ocean Drilling Program (ODP) Site 1051 (Blake Nose, off Florida) display well-defined orbital cycles, a detailed magnetic stratigraphy, and a suite of planktonic foraminiferal datums. We derived a cyclostratigraphy by using spectral analysis of high-resolution records of elemental concentrations obtained by an X-ray fluorescence (XRF) Core Scanner. XRF counts of iron serve as a proxy for the relative amount of terrestrial material. Sliding-window spectral analysis, bandpass filtering, and direct counting of precession and obliquity cycles yield minimum durations for magnetic polarity chrons C22 to C26 (~49 to ~61 Ma), calculations of sediment accumulation rates, as well as constraints on the timing of biostratigraphic and climatological events in the vicinity of the Initial Eocene Thermal Maximum (IETM). Durations of polarity chrons as represented in sediments drilled at Site 1051 were estimated using a conservative assignment of 41 k.y. for obliquity cycles and 21 k.y. for precession cycles. Combined polarity chrons C26r and C26n span 3.61 m.y., and chron C25r spans 1.07 m.y. Polarity chron C24r is estimated as 2.877 m.y. The interpretation of polarity chron C24n is ambiguous, but its duration is probably <1.23 m.y. Polarity chron C23r spans 0.53 m.y., chron C23n is 0.74 m.y., and chron C22r is 0.9 m.y. Spectral analysis through this interval indicates that spectral peaks shift through time and are related to changes in sedimentation rate in Site 1051. The sedimentation rates dramatically increased ~200 k.y. after the IETM and remained high for most of chron C24r.