Export of nutrient rich Northern Component Water preceded early Oligocene Antarctic glaciation

Abstract

Onset of North Atlantic deep water formation is thought to have coincided with Antarctic ice sheet growth about 34 million years ago. However, this timing is debated, in part due to questions over the geochemical signature of ancient Northern Component Water formed in the deep North Atlantic. Here we present detailed geochemical records from North Atlantic sediment cores located close to sites of deep water formation. We find that prior to 36 million years ago, the northwestern Atlantic was stratified, with nutrient-rich, low salinity bottom waters. This restricted basin transitioned into a conduit for Northern Component Water that began flowing southwards approximately one million years before initial Antarctic glaciation. The probable trigger was tectonic adjustments in subarctic seas that enabled increased exchange across the Greenland-Scotland Ridge. Increasing surface

Midlatitude Temperature Variations in the Oligocene to Early Miocene

“…Benthic foraminfera δ 13 C values denote an interesting Atlantic circulation feature of lower values in this northern site than in the southern Walvis Ridge (Site 1264; Figure e). This trend has been also demonstrated through the Eocene (Coxall et al, ; Cramer et al, ), and our data show that it continues through the Oligocene.…”

Phosphogenesis during the Cenozoic transition from greenhouse to icehouse conditions: Upper Oligocene to lower Miocene siliceous, phosphate, and organic‐rich sediments near La Purísima, Baja California Sur, Mexico

“…A further circumstance that may have catalysed phosphorite formation during these time periods is the focused return of phosphorus-enriched deep waters to the continental margin by an increase in the efficiency of coastal upwelling (Berger, 2007). This is often related to the isolation of the Antarctic continent and the onset of the Antarctic Circumpolar Current (ACC; Barker, Filippelli, Florindo, Martin, & Scher, 2007;Lyle, Gibbs, Moore, & Rea, 2007), in tandem with the progressive shift to North Atlantic Deep Water formation (NADW; Scher & Martin, 2008;Abelson & Erez, 2017;Coxall et al, 2018). These oceanographic changes may have led to an overall increase in bottomwater circulation, which improved the exchange between high-latitude and low-latitude deep waters.…”

Northeast Atlantic breakup volcanism and consequences for Paleogene climate change – MagellanPlus Workshop report

“…A significant consequence of the tectonic opening of the northeast Atlantic during the Paleogene and Neogene is the creation of ocean gateways linking the Arctic Ocean to the Atlantic through the Greenland, Iceland, and Norwegian seas (Nordic Seas). This process has been central to or part of previous scientific drilling expeditions in the northeast Atlantic region, and the results strongly indicate that these connections played a significant role in causing, or amplifying, environmental changes during the Cenozoic through their influence on water mass circulation (Laughton, 1975;Miller and Tucholke, 1983;Jakobsson et al, 2007;Boyle et al, 2017;Coxall et al, 2018;Vahlenkamp et al, 2018). Current questions are focusing again on the role and timing of mantle upwelling beneath Iceland in dynamically supporting regional bathymetry and the depth of oceanic gateways that control the strength of deep-water flow over geologic timescales (Miller and Tucholke, 1983;Poore et al, 2006;Parnell-Turner et al, 2014;Stärz et al, 2017), yet existing records are insufficient to move forward.…”

“…Magmatic intrusions can be of particu-lar importance as they may have the potential to release large amounts of greenhouse gases through contact metamorphism in a very short time (Berndt et al, 2016), and it remains plausible that the magmatism associated with the breakup of the northeast Atlantic triggered the Palaeocene-Eocene thermal maximum (PETM) (Svensen et al, 2004;Minshull et al, 2016). The subsequent long-term tectonic evolution of the northeast Atlantic through the Paleogene and Neogene created an ocean gateway linking the Arctic Ocean to global circulation that is likely to have played a significant role in causing, or amplifying, environmental changes through its influence on ocean circulation (Laughton, 1975;Miller and Tucholke, 1983;Jakobsson et al, 2007;Coxall et al, 2018).…”