This Monday 27.2.12

Charlie Main will be giving a practice talk for her upcoming presentation as part of the NOC Marine Life Talk lecutre series

Ecosystem effects of deep-water oil well blowouts

Deep-water oil well blowouts can bring large quantities of hydrocarbons into contact with the seabed and hence the deep-sea ecosystem. Scientists saw this when substantial quantities of oil were observed on the deep seafloor and also measured in the water following the Deepwater Horizon spill (Gulf of Mexico). Such events result in unknown  impacts on the way deep-sea organisms interact with their environment, in other words, on ecosystem function. Estimating and quantifying impacts of large-scale environmental disturbances is necessary to fully resolve our understanding of pollution effects on processes in the deep-sea. 

How can we predict potential effects of large, deep-sea oil spills in other areas of concern where deep-water drilling is happening? This talk will describe some interesting findings from the Gulf of Mexico spill that are shaping my PhD research here at the NOC. My own work is aimed at producing quantified estimates of the effects of oil on deep-sea ecosystem function. My methods include measuring oxygen usage (and hence carbon transfer) by living organisms in lab experiments and in the field. This is complemented by novel applications of existing computer models to aid prediction.

Introducing Rhubarb Methods!

Want to know more about a particular method of collection or analysis? Or perhaps you have experience with a technique not known to many?

Rhubarb talks are expanding to include a Rhubarb Methods session.

We are looking for speakers willing to give ≥5 minute talks about any method they are familiar with that others might like to know more about. These talks would be grouped in 3 or 4 to fill a 30 minute Rhubarb slot.

Possible topics include, but are not limited to: Electron microscopy, qPCR, elemental analysis, field collections/sampling techniques, biogeochemical models, etc.

Please get in touch if you are interested in speaking or have other ideas for topics.

Thanks,

The Rhubarb Team

Next week 20.2.12

In preparation for an upcoming conference, Maike Sonnewald will present a Rhubarb talk next Monday, 20.2.12 at 4:30pm in the PG lounge.

Oceanic dominance of interannual subtropical North Atlantic heat content variability

Abstract:

Ocean heat content varies on a range of timescales, with significant impact on the local climate through interactions with the atmosphere. This variability can be driven either by oceanic or atmospheric heat transport for a local body of water. To diagnose the relative contributions and respective timescales, this study uses a box model forced with GCM output to investigate the heat content variability of the upper 800 m of the subtropical North Atlantic from 26oN to 36oN. The ocean and air-sea heat flux data needed to force the box model is taken from a 19 year (1985 to

2006) simulation performed with the 1/12o version of OCCAM. The box model heat content is compared to the corresponding heat content in OCCAM for verification. The main goal of the study is to identify to what extent the interannual to subannual ocean heat content variability is of atmospheric or oceanic origin. To this end, the box model was subject to a range of scenarios forced either with the full (detrended) ocean and air-sea fluxes, or their deseasoned counterparts. This revealed that in all cases, the seasonal variability was dominated by the subannual component of the air-sea flux, which produced a seasonal range of ~0.41oC. However, on longer timescales the interannual oceanic heat transport dominates, with changes of up to ~0.16oC.

The technique is subsequently appplied to observational data. For the ocean heat fluxes, we use data from the RAPID programme at 26oN, and at 36oN heat transport is inferred using a linear regression model from the oceanic low-frequency transport in OCCAM. The air-sea flux from OCCAM is used for the period 2004 to 2006 when the RAPID timeseries and the OCCAM simulation overlap, and a climatology is used for the air-sea flux from

2006 onwards. The results confirm that on longer (>2 years) timescales the ocean dominates the ocean heat content variability. This work illustrates that oceanic divergence significantly impacts the ocean heat content variability on timescales relevant for applications such as hurricane forecasts, and thus that understanding the underlying mechanisms is of great socioeconomic importance.

INTERANNUAL VARIABILITY IN GLOBAL PHYTOPLANKTON PHENOLOGY

Harriet Cole will be presenting a practice talk for the ASLO conference this week.

INTERANNUAL VARIABILITY IN GLOBAL PHYTOPLANKTON PHENOLOGY

Harriet Cole, Stephanie Henson, Adrian Martin & Andrew Yool

Large areas of the world's oceans experience a significant seasonal cycle in phytoplankton biomass. The timing of the bloom affects ecosystem dynamics with implications for biogeochemical cycles and higher trophic levels. Phenological changes may additionally indicate climate change, as the physical processes that control timing alter in a warming world.

However, to understand future phenological changes we must first determine variability in timing and what drives it.

Here, phytoplankton phenology metrics such as bloom initiation and peak are calculated globally using satellite ocean colour data. The impact of gaps in the time-series is investigated using a global biogeochemical model that assimilates SeaWiFS data. We find that the missing data significantly alter estimations of bloom timing. This uncertainty is seen to vary spatially and between different methods of calculating the same metric.

We choose the most reliable metric based on this analysis to explore the relationships between interannual variability in phenology and underlying physical drivers, such as mixed layer depth and climate oscillation indices. Relating phenology to indicators of ocean variability offers new insights on the mechanisms that control bloom dynamics.