| |
| |
|
|
|
|
| |
 |
Pushing the frontiers of marine ecological modeling: where are we now and how can we move forward?
|
| |
|
|
Modeling seasonal and inter-annual variability of trophic transfer and 15N stable isotope enrichment within the planktonic food chain
Monday 7th @ 1050-1110, Conference Room 5
Sherwood. Lan Smith* , Research and Development Centre for Global Change Research, JAMSTEC, Yokohama, Japan
Yoshikazu Sasai, Research and Development Centre for Global Change Research, JAMSTEC, Yokohama, Japan
Chisato Yoshikawa, Department of Biogeochemistry, JAMSTEC, Yokosuka, Japan
Presenter Email: lanimal@jamstec.go.jp |
| The stable isotope 15N is widely used an indicator of trophic level, and has been incorporated into ecosystem models in order to understand nitrogen cycling and trophic transfer. However, such studies typically consider only the average enrichment per trophic level. We present a recently developed Trophic Level Variability (TLV) model of the dynamic fractionation of the stable isotope 15N in lower-trophic ecosystems of the North Pacific. The model accounts for the dynamics of trophic transfer from nutrients (nitrate and ammonium) to phytoplankton, and to two idealized zooplankton compartments representing herbivores and carnivores, respectively. The 15N signal of herbivores tracks that of phytoplankton, with a nearly constant offset, i.e., enrichment by a nearly constant factor. However, the modeled 15N difference between carnivores and herbivores varies seasonally, and depends on the mortality rate (turnover time or effective lifespan) of the carnivores. Seasonal variations of modeled 15N signals differ with trophic level because carnivores integrate the signal from their 15N uptake over longer timescales compared to herbivores. Thus, the model reproduces the lower observed variability of 15N for carnivorous zooplankton (chaetognaths) and the more variable 15N for largely herbivorous zooplankton (copepods). Our results imply that for interpreting observed 15N values, it is important to consider not only the average enrichment per trophic level, but also the dynamics of 15N fractionation and the timing of observations. We will also present some simulations illustrating how this modeling framework can be used to project changes in trophic transfer under climate change scenarios. |
|
|
|
|
|
|
|
|