Potential Impact of North Atlantic Climate Variability on Ocean Biogeochemical Processes

1. Potential Impact of North Atlantic Climate Variability on Ocean Biogeochemical Processes Yanyun Liu1,2 Collaborators: S.-K. Lee1,2, B.A. Muhling3, J.T. Lamkin4, D.B. Enfield1, M.A. Roffer5, F.E. Muller-Karger6 1UMiami/CIMAS, 2NOAA/AOML, 3Princeton U, 4NOAA/SEFSC, 5ROFFS, 6USF

2. Motivation and Background North Atlantic Ocean: one of the largest oceanic carbon sinks and heavily influenced by biological uptake (Sabine et al., 2004). Biogeochemical processes exhibit interannual-to-decadal fluctuations in response to large-scale internal climate variability (Gruber et al., 2002). Whether observed primary production change is a climate-change induced trend or natural climate variability? Require at least 40 years of continuous Chl measurements (Henson et al., 2010). Due to lack of consistent and long-term biological records, we use a global biogeochemical model to explore the impact of natural climate on Chl concentration in North Atlantic.

3. MOM-TOPAZ (ocean-sea ice-biogeochemistry model) Tracers for Ocean Phytoplankton with Allometric Zooplankton (TOPAZ)  Includes three phytoplankton groups (i.e., small, large and diazotrophic)  Consider 25 tracers (C, N, P, Si, Fe, DO, alkalinity ....)  Diazotrophic phytoplankton: fix atmospheric N2 directly  Includes the oceanic iron cycle including biological uptake and re-mineralization, particle sinking and scavenging and adsorption/desorption

4. MOM4-TOPAZ Configuration  Meridional resolution (1˚), zonal resolution varies between 1˚ in mid-latitudes and 1/3˚ at the equator.  50 vertical layers with thicknesses ranging from 10 m over the top 200 m to a maximum thickness of 250 m at 5500m depth.  Atmospheric forcing: Coordinated Ocean-ice Reference Experiment (CORE2).  Initialized from World Ocean Atlas with respect to temperature, salinity, nitrate, phosphate, silicate, etc.  The simulation was spun-up for 500 years with forcing from the CORE2 atmospheric forcing during 1948-1977.  The real-time simulation is run from 1948-2009.

5. MOM4-TOPAZ: Natural variability Surface chlorophyll is mostly underestimated in MOM4-TOPAZ, but, its spatial pattern is reasonably realistic.

6. MOM4-TOPAZ: Natural variability High Chl variability in the subpolar NATL, northeastern tropical ATL, and equatorial ATL.

7. MOM4-TOPAZ: Natural variability • Subpolar North Atlantic has high variability of Chl (STD/mean = 19%). • But, there is no long-term variability. • Subpolar North Atlantic Chl is significantly correlated with North Atlantic Oscillation (r = -0.3). • Subpolar North Atlantic Chl variability is largely link to light limitation of photosynthesis.

8. MOM4-TOPAZ: Natural variability

9. MOM4-TOPAZ: Natural variability

10. MOM4-TOPAZ: Natural variability

11. MOM4-TOPAZ: Natural variability • Dipole variability of Chl between northeastern tropical Atlantic and equatorial Atlantic (STD/mean = 34%). • Chl in the northeastern tropical Atlantic decreased greatly during 1960s and 1970s. It is significantly anti-correlated with AMO and AMM. • This region is one of the known habitats for Yellowfin Tuna (YFT) • Beardsley (1969), and Mendessohn & Roy (1986) reported links between SSTs/upwelling and YFT catch.

12. Chl in Northeastern tropical ATL Chl vs. AMO: -0.3 Chl vs. AMM: -0.5

13. MOM4-TOPAZ: Natural variability Increased trade wind ([-]AMM & [-]AMO) leads to increased upwelling of nutrients

14. MOM4-TOPAZ: Natural variability

15. MOM4-TOPAZ: Natural variability • Weak dipole variability of Chl between northeastern tropical Atlantic and equatorial Atlantic (STD/mean = 24%). • The variability is largely linked to Atlantic-Niño (r=-0.9)/AMM (r=0.6) and associated equatorial upwelling of nutrients • This region is one of the known habitats for Yellowfin Tuna.

16. MOM4-TOPAZ: Natural variability Increased trades ([+]AMM & [-]Atlantic-Niño) leads to increased upwelling of nutrient.

17. MOM4-TOPAZ: Natural variability

18. Natural variability of primary productivity in NATL • High Chl variability in subpolar NATL, northeastern tropical ATL, and equatorial ATL. • Subpolar NATL (light-limited)  Significantly correlated with NAO  Increased westerlies ([+] NAO) lead to deeper MLD • Dipole variability of Chl between northeastern tropical Atlantic and equatorial Atlantic: • Northeastern tropical ATL (nutrient limited)  Significantly correlated with AMM, and AMO  Increased trades ([-]AMM & [-]AMO) lead to increased upwelling of  nutrients • Equatorial ATL  Significantly correlated with AMM and Atlantic-Niño  Increased trades ([+]AMM & [-]Atlantic-Niño) leads to increased  upwelling of nutrients

19. Future Work • Use the updated MOM5-TOPAZ model with different forcing to further study the natural climate variability of biogeochemical processes in NATL. • Simulate the future changes of biogeochemical processes in NATL to better understand and compare the anthropogenic influences and natural variability. • Use downscaled regional ocean-biogeochemical model to study climate impact on the biogeochemical processes in NATL.

20. MOM4-TOPAZ Chl (RCP8.5) Reduce Chl in northeastern tropical ATL and equatorial ATL during the 21st century.