The sensitivity of the Eocene-Oligocene Southern Ocean to the strength and position of wind stress

The early Cenozoic opening of the Tasmanian Gateway (TG) and Drake Passage (DP), alongside the synergistic action of the westerly winds, led to a Southern Ocean transition from large, subpolar gyres to the onset of the Antarctic Circumpolar Current (ACC). However, the impact of the changing latitudinal position and strength of the wind stress in altering the early Southern Ocean circulation has been poorly addressed. Here, we use an eddy-permitting ocean model (0.25∘) with realistic late Eocene paleo-bathymetry to investigate the sensitivity of the Southern Ocean to paleo-latitudinal migrations (relative to the gateways) and strengthening of the wind stress. We find that southward wind stress shifts of 5 or 10∘, with a shallow TG (300 m), lead to dominance of subtropical waters in the high latitudes and further warming of the Antarctic coast (increase by 2 ∘C). Southward migrations of wind stress with a deep TG (1500 m) cause the shrinking of the subpolar gyres and cooling of the surface waters in the Southern Ocean (decrease by 3–4 ∘C). With a 1500 m deep TG and maximum westerly winds aligning with both the TG and DP, we observe a proto-ACC with a transport of ∼47.9 Sv. This impedes the meridional transport of warm subtropical waters to the Antarctic coast, thus laying a foundation for thermal isolation of the Antarctic. Intriguingly, proto-ACC flow through the TG is much more sensitive to strengthened wind stress compared to the DP. We suggest that topographic form stress can balance surface wind stress at depth to support the proto-ACC while the sensitivity of the transport is likely associated with the momentum budget between wind stress and near-surface topographic form stress driven by the subtropical gyres. In summary, this study proposes that the cooling of Eocene Southern Ocean is a consequence of a combination of gateway deepening and the alignment of maximum wind stress with both gateways.publishedVersio

Erosional unconformity or non-deposition? An alternative interpretation of the Eocene seismic stratigraphy offshore Wilkes Land, East Antarctica

The sedimentary stratigraphy along the conjugate Australian-Antarctic continental margins provide insights into their tectonic evolution as well as changes in paleoceanographic conditions in the Southern Ocean. A comprehensive network of multichannel seismic reflection data as well as geological information from drill cores have been used to interpret the stratigraphic evolution of these margins. However, a number of alternative seismic interpretations exist for the Antarctic side, particularly due to sparse drill core information. A prominent high-amplitude reflector observed along the margin, extending from the continental shelf to the foot-of-slope, is at the centre of debate. Recently, two major hiatuses (from 33.6 - 47.9 Ma and 51.06 - 51.9 Ma) were recovered by the IODP drill core U1356A offshore Wilkes Land and correlated to this prominent reflector. Previous seismic stratigraphic investigations interpreted this structure as an erosional unconformity and proposed different events as a possible cause for this formation, including first arrival of the continental glaciation at the coast at about 34 Ma, increase in spreading rate between Australia and Antarctica at about 45 Ma and drastic global sea level drop of 70 m at about 43 Ma. However, such a large-scale erosion must consequently lead to a re-deposition of a significantly large amount of sediment somewhere along the margins, but, to date, no such deposition is observed in the seismic reflection data. Here, we present an alternative seismo-stratigraphic interpretation based on correlation to the sedimentary structures along the Australian margin.We argue that the prominent unconformity is formed due to non-deposition of sediment between �47.8 and �33.6 Ma. The sedimentary units underlying this unconformity show strong similarities in structure, seismic characteristics and variation along the margin with sequences that are partly exposed to the seafloor at the foot of the Australian slope. On the Australian flank, the age of these exposed sediment sequences ranges from �65 Ma to �45 Ma. Low to no sedimentation from 45 Ma to the present-day offshore Australia has been interpreted to explain the exposure of these old sediment units. We propose that non-deposition occurred along both margins from �45 Ma, until large-scale glacial deposition started at 33.6 Ma along the Antarctic margin. Using our new interpretation, we create paleo-bathymetric reconstructions using the software BALPAL at �83 Ma, �65 Ma and �45 Ma. The resulting paleo-bathymetric maps provide essential information, e.g. for paleo–oceanographic and –climatic investigations in the Southern Ocean

„war etwas ganz tolles“ – Erzählungen über die Grenzöffnung 1989 im Kontext frame-semantischer und korpusbasierter Analysen

For more than 30 years, the inner-German border as a physical border between the GDR and FRG no longer exists. From a linguistic perspective, “unification” can be assumed. The linguistic differences between the former East and West Germans are smaller than those between the various German dialect speakers (cf. i. a. Hellmann 1984; Gärtig/Plewnia/Rothe 2010; Plewnia 2015). However, categories such as Ossi and Ostdeutsch or Wessi and Westdeutsch can still be found today, although the terms for the inhabitants of the GDR (Ossi, Ostdeutsch, Ostler etc.) are more productive. The physical inner-German border seems to have turned into a wall in people’s minds. This article takes up the current discourse and asks about the underlying patterns and frames that constitute this mental border or enable its reconstruction. Autobiographical narrative interviews with people of two age groups who grew up or were socialised at the former inner-German border serve as a basis for this

Linguistic patterns and frames in the context of the concept “wall in minds”

For more than 30 years, the inner-German border as a physical borderbetween the GDR and FRG no longer existed. From a linguistic perspective, unificationcan be assumed. The linguistic differences between the former East and West Germansare smaller than those between the different German dialect speakers. However,categories such as Ossi, East German or Wessi, West German can still be found today,although the terms for the inhabitants of the GDR (Ossi, Ostdeutsch, Ostler etc.) aremore productive. The physical inner-German border seems to turn into a wall inpeople's minds. This article takes up the current discourse and asks about theunderlying patterns and frames that constitute this mental border or enable itsreconstruction. Autobiographical narrative interviews with people of two age groupswho grew up or were socialised at the former inner-German border serve as a basis.For more than 30 years, the inner-German border as a physical borderbetween the GDR and FRG no longer existed. From a linguistic perspective, unificationcan be assumed. The linguistic differences between the former East and West Germansare smaller than those between the different German dialect speakers. However,categories such as Ossi, East German or Wessi, West German can still be found today,although the terms for the inhabitants of the GDR (Ossi, Ostdeutsch, Ostler etc.) aremore productive. The physical inner-German border seems to turn into a wall inpeople's minds. This article takes up the current discourse and asks about theunderlying patterns and frames that constitute this mental border or enable itsreconstruction. Autobiographical narrative interviews with people of two age groupswho grew up or were socialised at the former inner-German border serve as a basis

„war etwas ganz tolles“ – Erzählungen über die Grenzöffnung 1989 im Kontext frame-semantischer und korpusbasierter Analysen

For more than 30 years, the inner-German border as a physical border between the GDR and FRG no longer exists. From a linguistic perspective, “unification” can be assumed. The linguistic differences between the former East and West Germans are smaller than those between the various German dialect speakers (cf. i. a. Hellmann 1984; Gärtig/Plewnia/Rothe 2010; Plewnia 2015). However, categories such as Ossi and Ostdeutsch or Wessi and Westdeutsch can still be found today, although the terms for the inhabitants of the GDR (Ossi, Ostdeutsch, Ostler etc.) are more productive. The physical inner-German border seems to have turned into a wall in people’s minds. This article takes up the current discourse and asks about the underlying patterns and frames that constitute this mental border or enable its reconstruction. Autobiographical narrative interviews with people of two age groups who grew up or were socialised at the former inner-German border serve as a basis for this