Nitrogen isotope constraints on redox conditions in the North Pacific Ocean during the warm Pliocene Epoch

The Pliocene (2.6 to 5.3 Million years ago) is the most recent interval when Earth experienced atmospheric carbon dioxide concentrations (pCO2) above 400 ppmv (present-day level) and higher than modern global temperatures by (3-4° C). The arrangement of the continents was also alike present-day; therefore, the Pliocene makes a valuable potential analogue for predicting future climate change. Until recently, it was assumed that global warming would lead to sluggish overturned currents. Recent modeling, however, suggests that the Pliocene supported a Pacific Meridional Ocean Circulation (PMOC) with deep-water forming in the North Pacific where only intermediate water forms today.

SLIDE 1
Hello everyone,
Welcome and thank you for taking the time to watch my presentation today!
My name is Natasha Tagle & my research is over nitrogen isotope constraints on redox conditions in the North Pacific Ocean during the warm Pliocene Epoch. This was completed under the supervision of my awesome advisor Geoffrey Gilleaudeau.

SLIDE 2
You may be wondering why nitrogen isotopes in the ocean is important, or why it should matter? Well, let’s begin. It is critical for us to understand how the ocean-atmospheric system will respond to any future climate changes. We decided it was best to use a period of a warm climate to best study our question. Decreased ocean circulation can lead to negative impacts like a lack of O2 (oxygen) ventilation to the bottom of the ocean. In the diagram, you can see that both sides of display warm water, but there is no ocean circulation today. Unlike what I am proposing for the Pliocene 2.72 mya.

SLIDE 3
The samples used for this project come from IODP (International Ocean Discovery Program) and the core samples allocated are sites 1151A & 883B.
To have them prepped for nitrogen analysis they samples went through: a visual description, crushed them into a fine powder, weighed out 3 g of sample powder into a tube, acidified samples with hydrochloric acid to remove any carbonate material – and leaving it overnight, rinsed samples with ultrapure water to remove remaining acid, then left uncapped tubes to dry in an oven at 80 C overnight, reweigh to find amount of material lost to acidification, and finally re-crushed samples to be analyzed at the University of Maryland.

SLIDE 4
As you can see, this beautiful curve in my box and whisker plot of all the compiled data from my samples and other previous research data sets, this curve is representing the denitrification/or the change from a well-circulated deep ocean to non-deep ocean circulation environment. The two samples on the left side are from this project. The next two samples, 882A is very close in distance to my 883B core. Both of those are recorded during my period of this study and after 2.73 mya. The far-right shows a modern-day site with no deep ocean circulation.
In conclusion, based off the data collected and recorded throughout this research project support my hypothesis of deep-ocean circulation in the North Pacific Ocean during the Pliocene Epoch.