Natural Variability in a Changing Ocean: Emergence and Impacts

Seminar by Ms. Sarah Schlunegger from Princeton University

24 June 2019
KST 10:00 – 11:00

The Seminar is being held in Room 1010 (Jasmin) – Integrated mechanical engineering building. Click here for the campus map.

Anthropogenically-forced changes in the ocean are underway and critical for the ocean’s role as a carbon sink and marine habitat. Detecting such changes will require quantification of not only the magnitude of the change (anthropogenic signal) but also the natural variability inherent to the climate system (noise). This work uses Earth System Models (ESMs) to evaluate timescales over which anthropogenic signals in the contemporary ocean emerge from natural climate variability. 

We apply time-of-emergence (ToE) diagnostics to a Large Ensemble experiment of an ESM, providing both a conceptual framework for interpreting the detectability of anthropogenic impacts on the ocean carbon cycle and observational sampling strategies required to achieve detection. We find ToEs for different components of the ocean carbon cycle range from under a decade to over a century, a consequence of the time-lag between chemical and radiative impacts of rising atmospheric CO2 on the ocean. Processes sensitive to chemical changes emerge rapidly, such as impacts of acidification on the calcium-carbonate pump (10-20 years), and the invasion flux of anthropogenic CO2  into the ocean (20-30 years). Processes sensitive to the ocean’s physical state, such as the soft-tissue pump, which depends on nutrients supplied through circulation, emerge decades later (20-80+ years). 

Next, we evaluate the model- and scenario-sensitivity of ToEs through comparing Large Ensembles from 4 ESMs. We find ToEs are robust across models for variables that are tied directly to the rise in atmospheric CO2 – namely rising sea surface temperature and the invasion flux of anthropogenic CO2  into the ocean (ToE 20-30 years). For the soft-tissue pump, ocean color, and sea surface salinity, ToEs are longer (50+ years), less robust across ESMs, and more sensitive to the forcing scenario considered.