200 likes | 214 Views
Potential Impact of North Atlantic Climate Variability on Ocean Biogeochemical Processes. Yanyun Liu 1,2 Collaborators: S.-K. Lee 1,2 , B.A. Muhling 3 , J.T. Lamkin 4 , D.B. Enfield 1 , M.A. Roffer 5 , F.E. Muller-Karger 6
E N D
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
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.
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
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.
MOM4-TOPAZ: Natural variability Surface chlorophyll is mostly underestimated in MOM4-TOPAZ, but, its spatial pattern is reasonably realistic.
MOM4-TOPAZ: Natural variability High Chl variability in the subpolar NATL, northeastern tropical ATL, and equatorial ATL.
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.
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.
Chl in Northeastern tropical ATL Chl vs. AMO: -0.3 Chl vs. AMM: -0.5
MOM4-TOPAZ: Natural variability Increased trade wind ([-]AMM & [-]AMO) leads to increased upwelling of nutrients
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.
MOM4-TOPAZ: Natural variability Increased trades ([+]AMM & [-]Atlantic-Niño) leads to increased upwelling of nutrient.
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
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.
MOM4-TOPAZ Chl (RCP8.5) Reduce Chl in northeastern tropical ATL and equatorial ATL during the 21st century.