Abstract International Ocean Discovery Program (IODP) Expedition 382 in the Scotia Sea’s Iceberg Alley recovered among the most continuous and highest resolution stratigraphic records in the Southern Ocean near Antarctica spanning the last 3.3 Myr. Sites drilled in Dove Basin (U1536/U1537) have well‐resolved magnetostratigraphy and a strong imprint of orbital forcing in their lithostratigraphy. All magnetic reversals of the last 3.3 Myr are identified, providing a robust age model independent of orbital tuning. During the Pleistocene, alternation of terrigenous versus diatomaceous facies shows power in the eccentricity and obliquity frequencies comparable to the amplitude modulation of benthic δ 18 O records. This suggests that variations in Dove Basin lithostratigraphy during the Pleistocene reflect a similar history as globally integrated ice volume at these frequencies. However, power in the precession frequencies over the entire ∼3.3 Myr record does not match the amplitude modulation of benthic δ 18 O records, suggesting Dove Basin contains a unique record at these frequencies. Comparing the position of magnetic reversals relative to local facies changes in Dove Basin and the same magnetic reversals relative to benthic δ 18 O at North Atlantic IODP Site U1308, we demonstrate Dove Basin facies change at different times than benthic δ 18 O during intervals between ∼3 and 1 Ma. These differences are consistent with precession phase shifts and suggest climate signals with a Southern Hemisphere summer insolation phase were recorded around Antarctica. If Dove Basin lithology reflects local Antarctic ice volume changes, these signals could represent ice sheet precession‐paced variations not captured in benthic δ 18 O during the 41‐kyr world.
Thesis by publication.%%%%%%%%%%%%Chapter 1. General introduction – Chapter 2. Study, design, instrumentation and methodology – Chapter 3. A new approach to testing the agreement of two phytoplankton quantification techniques : microscopy and CHEMTAX – Chapter 4. Phytoplankton composition under contrasting oceanographic conditions : upwelling and downwelling (Eastern Australia) – Chapter 5. Environmental variables determine cross-shelf phytoplankton community structures : two case studies from the Kimberley and Coffs Harbour regions (Australia) – Chapter 6. Interactions between seasonality and oceanic forcing drive the phytoplankton variability in the tropical-temperate transition zone (~30°S) of Eastern Australia – Chapter 7. General discussion and conclusion.%%%%The East Australian Current (EAC) is the Western Boundary Current (WBC) of the South Pacific Gyre, transporting warm water from tropical to temperate latitudes along Eastern Australia. Due to climate change, the EAC is warming and strengthening, which is expected to impact on phytoplankton abundance, distribution and composition. This thesis aims at providing the first taxonomic phytoplankton time-series survey (May 2011 - September 2012) in the tropical-temperate transition zone of Eastern Australia (~30°S, Coffs Harbour). An interdisciplinary approach of oceanography, microscopy, phytoplankton pigment analysis through CHEMTAX and statistics was used. By applying this approach, the phytoplankton community was estimated and investigated under contrasting oceanographic conditions, along crossshelf gradients of environmental variables and throughout one annual cycle. The influence of the EAC on the shelf-scale and seasonal phytoplankton variability was examined in detail. Microscopy analysis revealed the abundance of 137 microphytoplankton taxa within 74 genera, including diatoms, dinoflagellates, silicoflagellates and Trichodesmium erythraeum. In addition, CHEMTAX determined the presence of pico- and nanophytoplankton, including cyanobacteria, cryptophytes, euglenophytes, haptophytes, pelagophytes and prasinophytes. Both microscopy and CHEMTAX revealed diatoms as being the most abundant phytoplankton taxon off Coffs Harbour. Shelf-scale phytoplankton abundance, distribution and composition were found to be driven by the highly variable oceanographic environment, and, on a seasonal scale, by the combination of the EAC and intrinsic seasonal cycles. Upwelling triggered two diatom blooms during December 2011 (Pseudo-nitzschia spp.) and September 2012 (Leptocylindrus danicus). This thesis has provided baseline information on interactions between oceanography and phytoplankton dynamics at ~30°S, Eastern Australia. The results from this survey are a key reference for future studies investigating changes in phytoplankton communities along the east Australian coast as a consequence of the strengthening EAC. Furthermore, the findings of this thesis find applicability in globally changing subtropical WBC systems. All of these systems are currently undergoing…
Paleontological data were collected using microscopes and recorded in the JRSO description software. All data for a species group (e.g., diatoms or nannofossils) were collected in a Microsoft Excel worksheet by hole. A zip file of the entire expedition's observations is also available.
Alkalinity was determined by Gran titration with an autotitrator (Metrohm 794 basic Titrino) using 0.1 M HCl at 20 degrees C. Report includes alkalinity, correction factor (if applicable), and pH.
Abstract With ongoing climate change, research into the biological changes occurring in particularly vulnerable ecosystems, such as Antarctica, is critical. The Totten Glacier region, Sabrina Coast, is currently experiencing some of the highest rates of thinning across all East Antarctica. An assessment of the microscopic organisms supporting the ecosystem of the marginal sea‐ice zone over the continental rise is important, yet there is a lack of knowledge about the diversity and distribution of these organisms throughout the water column, and their occurrence and/or preservation in the underlying sediments. Here, we provide a taxonomic overview of the modern and ancient marine bacterial and eukaryotic communities of the Totten Glacier region, using a combination of 16S and 18S rRNA amplicon sequencing (modern DNA) and shotgun metagenomics (sedimentary ancient DNA, sed aDNA). Our data show considerable differences between eukaryote and bacterial signals in the water column versus the sediments. Proteobacteria and diatoms dominate the bacterial and eukaryote composition in the upper water column, while diatoms, dinoflagellates, and haptophytes notably decrease in relative abundance with increasing water depth. Little diatom sed aDNA is preserved in the sediments, which are instead dominated by Proteobacteria and Retaria. We compare the diatom microfossil and sed aDNA record and link the weak preservation of diatom sed aDNA to DNA degradation while sinking through the water column to the seafloor. This study provides the first assessment of DNA transfer from ocean waters to sediments and an overview of the microscopic communities occurring in the climatically important Totten Glacier region.
We present a continuous ~7,000-year sedimentary record from Lashmars Lagoon, Kangaroo Island (Karti), southern Australia, from a region heavily impacted by drought and bushfires in recent decades. Records such as this are vital to contextualise current climatic and environmental shifts, particularly regarding the interplay between hydroclimate and fire-related disturbances in this ecologically sensitive area. We use high-resolution µX-ray fluorescence core scanning, complemented by bulk organic geochemistry and X-ray diffraction mineralogy of catchment soil and lake sediments to reconstruct past climate and catchment processes. Phases of elevated sediment organic matter content (inferred from high Br and total organic carbon) suggest increased lake freshening and productivity, and coincide with increased chemical weathering (inferred from high Al/K and kaolinite/illite and feldspars), likely reflecting the influence of wetter climates. Conversely, periods of high Ca correlate with biogenic carbonate inputs typical of brackish conditions, which we attribute to drier climates or a marine influence. From 7.0 ka, at the mid-Holocene sea level highstand, until 5.7 ka, we suspect Lashmars Lagoon was under virtually continuous influence from the sea. At 5.7 ka, we interpret the abrupt increase in sediment total organic carbon to reflect the severance of the connection to the sea, allowing organic material to accumulate. This, coupled with evidence of high inferred chemical weathering, suggests the climate was relatively wet at the time. After 5.4 ka, our data point to the establishment of drier conditions until the commencement of wetter climates at 4.5 ka. From 2.5 ka, however, drier climates prevailed again until present. Notably, the climate changes recorded in the sedimentary sequence at Lashmars Lagoon seem to be linked to the strength of the Leeuwin Current, which brings warm tropical waters to southern Australia and may well have been an important driver of rainfall on Kangaroo Island (Karti) over the past ~7,000 years.
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