Babette Hoogakker

Babette Hoogakker

Visiting Fellow

My research interests are in the application and interpretation of foraminiferal isotope and trace metals and flow vigour proxies, to study the interaction between the biogeochemical cycles, large-scale ocean circulation and climate change in the past.

As part of my NERC funded junior research fellowship¬† I have developed a proxy-method to reconstruct historical¬† deep water dissolved oxygen concentrations and respired carbon. This work shows that changes in ocean circulation and ventilation, combined with upper ocean productivity, in the deep Atlantic Ocean can potentially account for an importartant fraction (15 to 20%) of glacial atmospheric CO2 decrease (Hoogakker et al., 2015). A successive publication shows that extreme millennial cooling events that occurred during the last glacial, associated with the discharge of large scale iceberg armada’s in the North Atlantic were associated with a basin-wide decrease in dissolved oxygen concentrations (Hoogakker et al., 2016).

Also see http://www.nature.com/ncomms/2016/160331/ncomms11146/abs/ncomms11146.html showing results of the aplication of an exciting new redox sensitive element proxy (I/Ca) in planktonic foraminifera, suggesting the appearance of oxygen depletion in surface waters during the last ice age in waters that are well ventilated today. And see https://www.earth.ox.ac.uk/2016/03/reduced-oxygen-in-ice-age-antarctic-ocean-gives-clue-to-missing-atmospheric-carbon-dioxide/

 

SEMForams

Scanning electron microscope (SEM) images of planktonic foraminifera from the equatorial Pacific taken by Luke Jones for his 4th year project featuring Globigerinoides sacculifer (top left), Neogloboquadrina dutertrei (top right), Pulleniatina obliquiloculata (bottom left), and Globigerinoides ruber (bottom right).

Trace element incorporation in foraminiferal calcite has revolutionized our understanding of the effect of global climate change on seawater temperatures and nutrient concentrations. Salinity was once contemplated to have a key control on Mg uptake in foraminiferal calcite, which would have important implications for seawater temperature reconstructions that are based on Mg/Ca analyses. Research from the highly saline Red Sea showed that a large proportion of the salinity effect proposed in some studies must be diagenetic (overgrowth) in origin, and that it is possible to get to accurate Mg/Ca ratios in foraminiferal calcite using alternative methods; (Hoogakker et al., 2009; Rohling et al., 2008). Recent, conventional, reconstructions of seawater temperatures in the Labrador Sea show that warmer and fresher conditions during the early Holocene may have been a limiting factor in Labrador Sea Water convection during that time (Hoogakker et al., 2015).

Gruber  SEM image of cross profile of G. ruber specimen from the Red Sea.

Publications that utilize bottom-water flow speed reconstructions at current controlled locations provide insights into the coupled nature of circulation changes and global climate. Over glacial millennial climate oscillations the flow strength of the Western Boundary Undercurrent at 3 km, along the coast of NE America, is strongly correlated with Antarctic temperature changes; the first study to suggest that meltwater type events in the north Atlantic likely only perturbed the shallow intermediate-water overturning cell (Hoogakker et al., 2007). A coupling between Antarctic climate change and source-water contributions was established in a subsequent publication (Gutjahr, Hoogakker et al., 2010). Over the last 10,000 years, a strong coupling between strength of North East Atlantic Deep Water (fed by Iceland-Scotland Overflow Water) and climate exists, with stronger current strength during the early Holocene, coincident with the Holocene Climate Optimum (Hoogakker et al., 2011).

 

Lu, Z., Hoogakker, B.A.A. et al. Oxygen depletion recorded in upper waters of the glacial Southern Ocean. Nature Communications 7, article number 11146, doi:10.1038/ncomms11146.

 

Hoogakker, B.A.A., Singarayer, J., Smith, R., et al., 2016. Terrestrial biosphere changes over the last 120 kyr . Climates of the Past 12, 51-73, doi:10.5194/cp-12-51-2016

 

Hoogakker, B.A.A., Thornalley, D.F., Barker, S., 2016. Millennial changes in North Atlantic oxygen concentrations. Biogeosciences 13, 211-221, doi:10.5194/bg-13-211-2016

 

Hoogakker, B.A.A., Elderfield, H., Schmiedl, G., McCave, I.N., Rickaby, R.E.M., 2015. ‘Glacial-interglacial changes in bottom-water oxygen concent on the Portuguese margin’ Nature Geoscience 8 doi:10.1038/ngeo2317

 

Hoogakker, B.A.A., McCave, I.N., Elderfield, H., Hillaire-Marcel, C., Simstich, J., 2015. Holocene climate variability in the northwest Atlantic. Journal of the Geological Society Thematic set: Holocene Climate Change, doi:10.1144/jgs2013-097

 

Hoogakker, BAA, Downy, F, Andersson, M,¬† Chapman, MR, Elderfield, H, McCave, IN, Lenton, TM, Gruetzner, J, 2013 ‘Gulf Stream – subtropocal gyre properties across two Dansgaard-Oeschger cycles’ Quaternary Science Reviews 81, doi.org/10.1016/j.quascirev.2013.09.020

 

Hoogakker, BAA, Chapman, MR, McCave, IN, Hillaire-Marcel, C, Ellison, CRW, Hall, IR, Telford, RJ, (2011) ‘Dynamics of North Atlantic Deep Water masses during the Holocene’, Paleoceanography. pp. n/a-n/a doi: 10.1029/2011PA002155

 

Hoogakker, B.A.A., Elderfield, H., Crowhurst, S., Oliver, K. 2010. Benthic foraminiferal oxygen isotope offsets over the last glacial-interglacial cycle. Paleoceanography 25, doi:10.1029/2009PA001870

 

Oliver, K., Hoogakker, B.A.A., Crowhurst, S., Henderson, G., Rickaby, R., Elderfield, H., Edwards, N. A   2010. A synthesis of marine sediment core d13C data over the last 150,000 years. Climates of the Past 5, 2497-2554, doi:10.5194/cp-6-645-2010

 

Hoogakker, BAA, Klinkhammer, GP, Elderfield, H, Rohling, EJ, Hayward, C, (2009) ‘Mg/Ca paleothermometry in high salinity environments’, Earth and Planetary Science Letters. pp. 583-589 doi: 10.1016/j.epsl.2009.05.027