Toward improved understanding of mass and property fluxes through Bering Strait Jaclyn Clement Kinney 1, Wieslaw Maslowski 1, Mike Steele 2, Jinlun Zhang 2, Rebecca Woodgate 2 1 Naval Postgraduate School, Monterey, CA 2 Applied Physics Laboratory, Univ. Washington, Seattle, WA

Courtesy NASA/JPL Primary goals of this work: Intercomparison of the volume, heat and freshwater fluxes through Bering Strait. Using model results to test assumptions (based on imperfect, spotty data) made by observationalists.

Volume and property fluxes are addressed by 2 modeling groups and 1 observational group Observational results provided by UW (Woodgate et al.) moored instruments placed ~10 m above the bottom eastern (since 1991) and western (?_?) channels and north of the strait (since 1991) very limited access to the western channel of Bering Strait – Russian waters extrapolations are made from the point measurements to total fluxes across the strait Calculations of heat and freshwater fluxes data used a reference temperature of -1.9 o C for heat fluxes, so we are attempting to do the same freshwater fluxes are referenced to 34.8

UW models (PIOMAS and BESTMAS) POP (ocean) and TED (ice) NCEP/NCAR reanalysis forcing horizontal resolution is ~22 km (PIOMAS) and ~7 km (BESTMAS), 30 vertical levels new BESTMAS run with minimum ocean depth of 15 m (instead of 30 m) and widened Bering Strait NPS model (NAME) based on POP (ocean) and Zhang-Hibler (ice); transitioning to CICE (ice) daily ECMWF forcing ~9km horizontal resolution, 45 vertical levels, 10 m minimum ocean depth * comparisons are between model cross-sections and data from a single mooring

A3 A1 A2 A3 A1 A2 A3 A1 A2 Bathymetry representation in the 3 models

26-yr mean velocity vertical section PIOMAS is very coarse BESTMAS and NPS are higher resolution NPS model has more variable bathymetry a lot of horizontal shear in all significant vertical shear in NPS

Velocity contours from current meter data (Coachman et al., 1975) highest speeds tend to be found in the eastern channel the pattern of horizontal shear in the Bering Strait seems to be relatively invariant a velocity minimum West of Fairway Rock several cases of local flow reversal in the upper layer

Time series of monthly mean volume transport, heat flux, and freshwater transport similar amount of variability in volume and freshwater between the models standard deviations for volume are Sv standard deviations for freshwater are mSv more variability in heat for UW models due to higher summer time peaks standard deviations for heat are 6 for NPS and 8/12 for UW 5-10% difference in heat flux values due to choice of Tref

Annual cycle of volume transport, heat flux, and freshwater transport volume transport stronger annual cycle in data; peaks in Jun NPS and PIOMAS peak in July BESTMAS peaks in May heat flux similar distribution for all models, except PIOMAS has much higher summer peaks freshwater transport similar distributions all 3 have peaks in July and minimums in March

Anomalies of volume transport, heat flux, and freshwater transport anomalies after removing the annual cycle strong correlations between the NPS and UW models (r = ); significant at 1% level no long-term trends are apparent

Annual means of volume transport, heat flux, and freshwater transport model values are within a few tenths of a Sv of the data at A3, however there is no strong correlation PIOMAS heat flux is much higher than the other 2 models annual means of freshwater transport are most similar

Temperature vertical sections Aug 2007 CTD temperature DATA (Woodgate et al.)

Salinity vertical sections Aug 2007 CTD temperature DATA (Woodgate et al.)

Monthly means of temperature and salinity strong annual cycle in temperature UW models show a much higher mean temperature than NPS and data (NCEP is warmer…) data are from ~10m above the bottom…so means would be warmer and fresher standard deviations of temperature are 1.66 (NPS), 1.78 (A3), 2.90 (PIOMAS), and 2.85 (BESTMAS) standard deviations of salinity are very similar for NPS, PIOMAS, and A3 ( ), higher for BESTMAS (0.78)

Annual cycles of temperature and salinity with data ( ) Temperature data is most similar to the NPS model UW summertime peaks are too high Salinity data is similar to PIOMAS and NPS NPS is a bit to fresh in summer and PIOMAS is a bit too saline in winter BESTMAS is much too saline in winter/spring

Anomalies of temperature and salinity with data Temperature Correlations NPS & A3 = 0.32* PIOMAS & A3 = 0.34* BESTMAS & A3 = Salinity Correlations NPS & A3 = 0.54* PIOMAS & A3 = 0.58* BESTMAS & A3 = 0.47*

Annual means of temperature and salinity with data Temperature there appears to be a (possibly) similar pattern in the annual mean temperature at A2/A3 and the model results between (e.g. the decrease between ) however, the UW temperatures are too high and the NPS variability is too low Salinity the NPS annual mean salinities have similar variability as the data at A3 for UW annual mean salinities are somewhat similar (e.g. show a peak one year later in 2000 vice 1999)

ParameterNPS mean PIOMAS mean BESTMAS mean Volume (Sv) Heat (TW) tref=- 1.9/-1.8 (UW) Freshwater (mSv) sref= Mean T Mean S Long-term model means UW models have higher transport than the NPS model by ( Sv) (range is only up to 10% of the 3-model mean) UW models, especially PIOMAS, have higher heat fluxes than NPS (large spread among heat fluxes, up to 35% of the 3-model mean) Freshwater fluxes are most similar between the models (range is only up to 15% of the 3-model mean)

ParameterNPS mean PIOMAS mean BESTMAS mean observations mean* Volume (Sv)0.64 (0.87) Heat (TW) tref=- 1.9/-1.8 (UW) Freshwater (mSv) sref= Mean T Mean S Long-term model and DATA* means PIOMAS most closely matches the data long-term mean of volume transport observations are calculated as velocity at one point (near-bottom at A3 north of the strait) multiplied by 2.6km 2 (cross-sectional area) * observed data are for ~10m above the bottom when NPS results are calculated the same way as observations, the volume transport is 0.87 Sv for (shown in parenthesis); other calculations would likely change, as well observed heat flux is most similar to BESTMAS and NPS results models are producing similar freshwater fluxes as the observations T and S are higher than observations for UW models and slightly lower for NPS models (method of calculation will be corrected for models)

Future Work We hope to be able to answer questions such as: “Why are the observations different from the model results?” “Can we use the model results to improve the assumptions made by observationalists?”