Benthic megafaunal composition at the Arctic deep-sea observatory HAUSGARTEN

The Long-Term Ecological Research (LTER) observatory HAUSGARTEN, in the eastern Fram Strait, provides us the valuable ability to study the composition of benthic megafaunal communities through the analysis of seafloor photographs. This, in combination with extensive sampling campaigns, which have yielded a unique data set on faunal, bacterial, biogeochemical and geological properties, as well as on hydrography and sedimentation patterns, allows us to address the question of why variations in megafaunal community structure and species distribution exist within regional (60-110 km) and local (<4 km) scales. Here, we present first results from the latitudinal HAUSGARTEN gradient, consisting of three different stations (N3, HG-IV, S3) between 78°30'N and 79°45'N (2351 - 2788 m depth), obtained via the analysis of images acquired by a towed camera (OFOS - Ocean Floor Observation System) in 2011. We assess variability in megafaunal densities, species composition and diversity as well as biotic and biogenic habitat features, which may cause the patterns observed. While there were significant regional-scale differences in megafaunal composition and densities between the stations (N3 = 26.74 ± 0.63; HG-IV = 11.21 ± 0.25; S3 = 18.34 ± 0.39 individuals/m**2), significant local differences were only found at HG-IV. Regional-scale variations may be due to the significant differences in ice coverage at each station as well as the different quantities of protein available, whereas local-scale differences at HG-IV may be a result of variation in bottom topography or factors not yet identified.

Investigation of Quaternary diatoms in sediment core CRP-1 from the Ross Sea, Antarctica

In the first season of drilling, the Cape Roberts Project (CRP) recovered one drillcore (CRP-l) from Roberts Ridge in western McMurdo Sound, Ross Sea, Antarctica Diatom biostratigraphy places the upper six lithostratigraphic units (Units 1.1, 2.1, 2.2, 2.3, 3.1, and 4.1) of CRP-l (0.0 to 43.15 mbsf) within the Quaternary. Both non-marine and marine Quaternary diatoms occur in variable abundance in the Quaternary interval of CRP- 1 Biostratigraphic data resolve two Quaternary time slices or events within CRP-1. Marine diatom assemblages in Units 4.1 and 3.1 represent sedimentation within the diatom Actinocyclus ingens Zone (1.35 to 0.66 Ma). Further refinement of the age of Unit 3.l places deposition in the interval 1.15 to 0.75 Ma based on the common occurrence of Thalassiosira elliptipora and correlation to the Southern Ocean acme of this taxon The absence of ActiActinocyclus ingens and the presence ot Thalassiosira antarctica in Unit 2.2 require a younger zonal assignment for this interval, within the diatom Thalassiosira lentiginosa Zone (0.66 to 0.0 Ma). A new diatom species. Rouxia leventerae, is described from marine assemblages of Units 2.2, 2.3, 3.1, and 4.l. Lithostratigraphic Unit 3.1 (33.82 to 31.89 mbsf) is a bryozoan-dominated skeletal-carbonate facies. Low abundance of Fragilariopsis curta and Fragilariopsis cylindrus within this unit combined with the relatively high abundance of species associated with open water indicates deposition in waters that remained ice free for much or all of the year Diatom assemblages suggest carbonate deposition in Unit 3.1 is linked to a significant early Pleistocene event in McMurdo Sound, when elevated surface-water temperatures inhibited the formation of sea ice.

(Appendix) Benthic foraminifera distribution of upper Creatceous and Paleocene at DSDP Hole 72-516F

Benthic foraminifers of the Coniacian-Santonian through the Paleocene were recovered from a continuous pelagic carbonate section from Hole 516F on the Rio Grande Rise. Sixty-five genera and 153 species have been identified, most of which have been reported from other localities. Bathyal depths are reflected in the benthic assemblages dominated by gavelinellids (Gavelinella beccariiformis, G. velascoensis), Nuttallides truempyi, and various gyroidinids and buliminids. Rapid subsidence during the Coniacian-Santonian from nearshore to upper to middle bathyal depths was followed by much reduced subsidence, with the Campanian-Paleocene interval accumulating at middle bathyal to lower bathyal depths. A census study based on detailed sampling reveals major changes in benthic faunal composition at the Cretaceous/Tertiary boundary transition. It was a time of rapid turnover, with the extinctions of numerous species and the introduction of many new species. Overall, species diversity decreases about 20%, and approximately one-third of latest Maestrichtian species do not survive to the end of the Cretaceous. This shift indicates a significant environmental change in the deep sea, the precise nature of which is not apparent from the foraminifers or their enclosing sediments.

Biostratigraphy of sediment core CRP-3 from the Ross Sea, Antarctica

Early Oligocene siliceous microfossils were recovered in the upper c. 193 m of the CRP-3 drillcore. Although abundance and preservation are highly variable through this section, approximately 130 siliceous microfossil taxa were identified, including diatoms, silicoflagellates, ebridians, chrysophycean cysts, and endoskeletal dinoflagellates. Well-preserved and abundant assemblages characterize samples in the upper c. 70 m and indicate deposition in a coastal setting with water depths between 50 and 200 m. Abundance fluctuations over narrow intervals in the upper c. 70 mbsf are interpreted to reflect environmental changes that were either conducive or deleterious to growth and preservation of siliceous microfossils. Only poorly-preserved (dissolved, replaced, and/or fragmented) siliceous microfossils are present from c. 70 to 193 mbsf. Diatom biostratigraphy indicates that the CRP-3 section down to c. 193 mbsf is early Oligocene in age. The lack of significant changes in composition of the siliceous microfossil assemblage suggests that no major hiatuses are present in this interval. The first occurrence (FO) of Cavitatus jouseanus at 48.44 mbsf marks the base of the Cavitatus jouseanus Zone. This datum is inferred to be near the base of Subchron C12n at c. 30.9 Ma. The FO of Rhizosolenia antarctica at 68.60 mbsf marks the base of the Rhizosolenia antarctica Zone. The FO of this taxon is correlated in deep-sea sections to Chron C13 (33.1 to 33.6 Ma). However, the lower range of R. antarctica is interpreted as incomplete in the CRP-3 drillcore, as it is truncated at an underlying interval of poor preservation: therefore, an age of c. 33.1 to 30.9 Ma is inferred for interval between c. 70 and 50 mbsf. The absence of Hemiaulus caracteristicus from diatom-bearing interval of CRP-3 further indicates an age younger than c. 33 Ma (Subchron C13n) for strata above c. 193 mbsf. Siliceous microfossil assemblages in CRP-3 are significantly different from the late Eocene assemblages reported CIROS-1 drillcore. The absence of H. caracteristicus, Stephanopyxis splendidus, and Pterotheca danica, and the ebridians Ebriopsis crenulata, Parebriopsis fallax, and Pseudoammodochium dictyoides in CRP-3 indicates that the upper 200 m of the CRP-3 drillcore is equivalent to part of the stratigraphic interval missing within the unconformity at c. 366 mbsf in CIROS-1.

Diatom biostratigraphy of sediments from the Kerguelen Plateau, Southern Ocean

The biostratigraphic distribution and abundance of lower Oligocene to Pleistocene diatoms is documented from Holes 747A, 747B, 748B, 749B, and 751A drilled during Ocean Drilling Program Leg 120 on the Kerguelen Plateau in the southeast Indian Ocean. The occurrence of middle and upper Eocene diatoms is also documented, but these are rare and occur in discrete intervals. The recovery of several Oligocene to Pleistocene sections with minimal coring gaps, relatively good magnetostratigraphic signatures, and mixed assemblages of both calcareous and siliceous microfossils makes the above four Leg 120 sites important biostratigraphic reference sections for the Southern Ocean and Antarctic continent. A high-resolution diatom zonation divides the last 36 m.y. into 45 zones and subzones. This zonation is built upon an existing biostratigraphic framework developed over the past 20 yr of Southern Ocean/Antarctic deep-sea coring and drilling. After the recent advances from diatom biostratigraphic studies on sediments from Legs 113, 114, 119, and 120, a zonal framework for the Southern Ocean is beginning to stabilize. The potential age resolution afforded by the high-diversity diatom assemblages in this region ranks among the highest of all fossil groups. In addition to the 46 datum levels that define the diatom zones and subzones, the approximate stratigraphic level, age, and magnetic anomaly correlative of more than 150 other diatom datums are determined or estimated. These total 73 datum levels for the Pliocene-Pleistocene, 67 for the Miocene, and 45 for the Oligocene. Greater stratigraphic resolution is possible as the less common and poorly documented species become better known. This high-resolution diatom stratigraphy, combined with good to moderately good magnetostratigraphic control, led to the recognition of more than 10 intervals where hiatuses dissect the Oligocene-Pleistocene section on the Kerguelen Plateau. We propose 12 new diatom taxa and 6 new combination

Diatoms in Paleocene sediments of the southwestern South Atlantic

The taxonomy and stratigraphy of pelagic Paleocene diatoms from ODP Sites 698, 700, and 702 and DSDP Site 524 in the South Atlantic and DSDP Site 214 in the Indian Ocean are presented, as well as paleogeographic and paleoecologic implications. Eleven new species and one new variety are described and one new combination is proposed: Coscinodiscus cruxii sp. nov. Grunowiella palaeocaenica var. alternans var. nov. Hemiaulusl beatus sp. nov. Hemiaulusl ciesielskii sp. nov. Hemiaulusl conicus sp. nov. Hemiaulus kristoffersenii sp. nov. Hemiaulus nocchiae sp. nov. Hemiaulusl oonkii sp. nov. Hemiaulusl velatus sp. nov. Triceratium gombosii sp. nov. Trochosira gracillima comb. nov. Trochosira marginata sp. nov. Trochosira radiata sp. nov. Hole 700B provides one of the most continuous diatomaceous Paleocene profiles known. Stratigraphic ranges of diatom species from this and other Southern Hemisphere sites are calibrated against calcareous microfossil zones. The first-appearance datums of Triceratium gombosii, Hemiaulus incurvus, and Triceratium mirabile in Paleocene deep-sea sediments are useful for regional stratigraphic correlations. Quantitative analysis of the biosiliceous microfossil groups (diatoms, silicoflagellates, radiolarians, and archaeomonadaceae) shows that preservation of diatoms is confined primarily to the upper Paleocene (planktonic foraminifer Zones P3 and P4 and calcareous nannofossil Zones upper NP5 to lower NP9). In the lower Paleocene only short intervals in Hole 700B are diatomaceous. A correlation between the degree of silica diagenesis and the calcium carbonate content of the sediment is not obvious. Diatom species analysis reflects changes in the paleoenvironment between island-related upwelling conditions with highly diverse and well-preserved diatom assemblages and less productive periods resulting in less wellpreserved diatom assemblages with a higher content of robust neritic diatoms.

Calcareous nannofossils and planktonic foraminifera of ODP Hole 132-810C

The 136 m of calcareous oozes recovered in Hole 810C span the interval from upper Maastrichtian to middle Pleistocene. Three major hiatuses interrupt the sequence, with the topmost part of the Maastrichtian through the entire lower Paleocene, most of the lower Eocene, and the entire middle Eocene through most of the middle Miocene missing. Severe reworking and displacement affected the lower part of the succession from the Maastrichtian through the middle Miocene. Reworking and displacement gradually decreased in the upper portion. Calcareous nannofossil biostratigraphy enabled us to calibrate precisely the nearly complete magnetic reversal sequence of the Pliocene to the late Pleistocene. Two minor hiatuses detected by calcareous nannofossils across the Pliocene/Pleistocene boundary and in the upper lower Pleistocene, respectively, resulted in shortening of the Olduvai and Jaramillo Events within the Matuyama Chron of the magnetic reversal sequence.

Middle Miocene to Quaternary diatom biostratigraphy of DSDP Site 90-594

A diatom biostratigraphy is presented for middle Miocene through Quaternary sediments recovered from the Chatham Rise east of New Zealand's South Island. The upper 590 m of the 639.5-m composite-section Site 594 represents approximately 16 m.y. and is characterized by moderately to very poorly preserved diatoms of antarctic to temperate affinity. Pliocene through Quaternary assemblages are poorly preserved and dominated by antarctic-subantarctic species which provide detailed biostratigraphic control. Recognized are 11 of 14 zones of the middle upper Miocene to Quaternary Neogene Southern Ocean diatom zonation (NSD 7-NSD 20) of Ciesielski (1983; this chapter). Four Neogene Southern Ocean diatom zones (NSD 3-NSD 6) are recognized in the lower middle Miocene to middle upper Miocene of Site 594. Assemblages of this interval have a mixed high-latitude and temperate affinity; however, poor preservation limits correlation to high- and temperate-latitude zonal schemes. Neogene North Pacific diatom zones and subzones of NNPD 3 through NNPD 5 (Barron, in press, b) are correlated to Neogene Southern Ocean diatom zones NSD 3 through NSD 7: the upper portions of the Actinocyclus ingens Zone (NNPD 3) is correlative to the upper Nitzschia maleinterpretaria Zone (NSD 3); the Denticulopsis lauta Zone (NNPD 4) and Subzones a and b are correlative to the lower Coscinodiscus lewisianus Zone (NSD 4); and the D. hustedtü-D. lauta Zone (NNPD 5) and its Subzones a through d encompass the upper C. lewisianus Zone (NSD 4), N. grossepunctata Zone (NSD 5), N. denticuloides Zone (NSD 6), and the lower D. hustedtii-D. lauta Zone (NSD 7). A major disconformity spans the late Gilbert to early Gauss Chron (3.9-2.8 Ma). A second disconformity brackets the Miocene/Pliocene boundary; the section missing covers late Chron 5 and the early Gilbert chron (5.5-4.6 Ma). The remainder of the siliceous-fossil-bearing Miocene sediments at Site 594 appear to be correlative to lower paleomagnetic Chronozone 5 through upper Chronozone 16. Uppermost lower Miocene or lowermost middle Miocene sediments in the basal 50 m of Hole 594A are barren of diatoms.

Paleocene and Eocene diatom biosttarigraphy of ODP Hole 121-752A, eastern Indian Ocean

The Paleocene/Eocene boundary was recovered for the first time in diatom-bearing sediments at Broken Ridge, Site 752. Diatom assemblages are documented throughout the 180-m-thick sequence of upper Paleocene to lower Eocene sediments. Age control available from magnetostratigraphy, calcareous nannofossils, and planktonic foraminifers allows calibration of diatom datum levels to absolute time. A partly new/partly revised diatom zonation is proposed for the Paleocene/early Eocene based on the results of Site 752 and consideration of other studies. The diatom zones are defined as follows (from the youngest to the oldest): Pyxilla gracilis Zone (first occurrence of Craspedodiscus undulatus to first occurrence Pyxilla gracilis); Hemiaulus incurvus Zone (first occurrence Pyxilla gracilis to first occurrence Hemiaulus incurvus); Hemiaulus peripterus Zone (first occurrence Hemiaulus incurvus to first occurrence Hemiaulus peripterus var. peripterus). Three new taxa are described: Anaulus fennerae n. sp., Stictodiscus bipolaris n. sp., and Hemiaulus peripterus var. longispinus n. var.

Occurrence and abundance of diatoms at DSDP Holes 72-515B and 72-516F

Samples from the upper Oligocene and lower Miocene of Holes 515B (Brazil Basin) and 516F (Rio Grande Rise) were examined for fossil marine diatom content. The preservation of the diatoms was poor and the species diversity low in both holes. However, it was possible to zone portions of the intervals studied using the zonation proposed by Gombos and Ciesielski (1983), which is based, as far as possible, on common and robust species. Thus, the interval in Hole 515B represented by Cores 515B-15 and 515B-16 is assigned to the Coscinodiscus rhombicus Zone and the interval represented by Cores 515B-17 through 515B-44 is assigned to the Rocella gelida Zone. The C. rhombicus Zone is early Miocene in age and the R. gelida Zone is late Oligocene to early Miocene in age. In Hole 516F the interval represented by Cores 516F-6 through 516F-10 is assigned to the R. gelida Zone Gate Oligocene to early Miocene), and the interval represented by Cores 516F-11 through 516F-15 is assigned to the Triceratium groningensis Zone (late Oligocene). Two new fossil diatom taxa are defined herein: Coscinodiscus lewisianus Greville f. concavus n. f. and Rocella semigelida n. sp.