Sangil Kim

Connectivity and larval dispersal along the Oregon coast estimated by numerical simulations

[1] Connectivity and larval dispersal is explored off the Oregon coast during the summer upwelling season of 2001 using numerical ocean circulation simulations. The study region, with strong wind‐driven currents and variable topography, is modeled using the Regional Ocean Modeling System (ROMS) forced by the Coupled Ocean Atmosphere Mesoscale Prediction System. A large number of passive particles as models of planktonic larvae are released daily for 120 days from 1 May to 28 August at depths of 1, 7, 15, 20, 50, and 75 m at every grid point shoreward of the 200 m isobath (on average 32 km offshore). The particles are transported by the three‐dimensional currents of the model simulation. The competency time window for larval settlement is assumed to be in between days 15 and 35 after larvae are released. Larval settlement occurs at the shallowest location during the competency time window. Connectivity matrices reveal that some of the places of highest retention are similar to the proposed Oregon marine reserve sites, especially Cape Perpetua. The Heceta Bank region has high probabilities as both a source and a destination for settled larvae. Larvae released in the Heceta Bank region often settle at higher latitudes than their release location. There are strong correlations between the number of settled larvae shallower than the 50 m isobath and a 6 to 8 day running mean of the alongshore wind stress. Larvae are retained near the shore when the winds, averaged over the previous 6 to 8 days, are relaxed or downwelling favorable.

Evaluation of a regional ocean reanalysis system for the East Asian Marginal Seas based on the ensemble Kalman filter

This study introduces the East Asian Marginal Seas (EAMS) reanalysis system and evaluates its products from 1982 to 2006. The EAMS reanalysis system consists of an ocean circulation model with 0.25° horizontal grid spacing and a data assimilation module. Temperature profiles taken by ship and Argo floats as well as satellite-borne sea surface temperature (SST) were assimilated into the model by applying the ensemble Kalman filter every 7 days. The reanalyzed oceanic fields were compared with ones by the control run without data assimilation to assess the impact of the data assimilation. The assimilative model significantly improved the horizontal structures of SST, sea surface height (SSH), vertical structure of temperature, and volume transports through the major straits. Root-mean-square error (RMSE) of SST decreased from 1.0 to 0.6°C. Horizontal and vertical distribution of subsurface temperature was corrected close to the observed values. High SSH variability in the south of Japan and in the Kuroshio extension region was partially restored. Overshooting of the Kuroshio Current and the East Korea Warm Current was suppressed to the south by the data assimilation. SSH and surface circulation in the Oyashio region and in the East Sea (also known as the Sea of Japan) recovered, which corrected the sea level difference between the East Sea and the Pacific Ocean and produced realistic transport through the Korea Strait. The reanalysis well resolved transport through the Korea Strait. The correlation coefficient with the transport based on an Acoustic Doppler Current Profiler measurement was 0.70 and the RMSE was 0.37 Sv (106 m3/s), whereas those were 0.59 and 0.43 Sv in the control run, respectively. The EAMS reanalysis dataset may help us to understand circulation variations in the marginal seas and to investigate factors controlling volume and heat transport.

Potential errors in fiber length measurements resulting from lever arm rotation during mechanical testing of muscle cells

In single muscle cell preparations fibers are often suspended between connectors, extending perpendicularly from a force transducer, and the lever arm of a torque motor. The fiber does not move along a horizontal plane when shortened or lengthened by lever arm rotation. An error from the true length (TL) is introduced if the expected length (EL) is calibrated along this horizontal optical plane. Lever arm length (LAL), initial fiber length (FL(i)), connector length (CL), and the magnitude of EL all contribute to this error. A mathematical model was used to determine the TL during shortening (0.96-0.80 FL(i)) and lengthening (1.10-1.50 FL(i)) at a constant LAL of 13.6mm. CL had the greatest impact on error. For FL(i) = 2mm at the longest CL modeled (15 mm), an expected shortening of 0.20 FL(i) produced a true shortening of ∼ 0.17 FL(i), and an expected stretch to 1.50 FL(i) resulted in a true stretch to almost 1.60 FL(i). Under these conditions, the true sarcomere length would be 4% and 6% longer than expected during shortening and lengthening, respectively. Because of their non-linear nature, length errors at long CLs may result in an over-estimation of unloaded shortening velocity during slack tests and a left-ward shift in the passive tension-fiber length relationship at long fiber lengths. Measurement errors decreased dramatically with shorter CLs, becoming negligible (<1%) at CL = 3mm. We recommend that investigators keep CL as short as possible. Alternatively, we provide a method for adjusting the magnitude of the EL to yield a desired TL.

Comparison of Ensemble-Based Filters for a Simple Model of Ocean Thermohaline Circulation

The performance of ensemble-based filters such as Sequential Importance Resampling (SIR) method, Ensemble Kalman Filter (EnKF), and Maximum Entropy Filter (MEF) are compared when applied to an idealized model of ocean thermohaline circulation. The model is a stochastic partial differential equation that exhibits bimodal states and rapid transitions between them. The optimal filtering result against which the methods are tested is obtained by using the SIR filter with N=104 for which the method converges. The numerical results reveal advantages and disadvantages of each ensemble-based filter. SIR obtains the optimal result, but requires a large sample size, N⩾ 103. EnKF achieves its best result with relatively small sample size N=102, but this best result may not be the optimal solution. MEF with N=102 achieves the optimal results and potentially is a better tool for systems that exhibit abrupt state transitions.

Stipe Length as an Indicator of Reproductive Maturity in the Kelp Ecklonia cava

We conducted testing to determine whether stipe length is a useful indicator of reproductive maturity in the kelp Ecklonia cava, a species that plays a pivotal role in ecosystem functioning and services in subtidal areas. Approximately 100 sporophytes with stipes of various lengths were collected during the fertile period (July–November, 2013). We investigated the relationships between stipe length and other morphological characteristics to determine whether stipe length could indicate the age of reproductive maturity. Primary blade length, longest blade length, thallus height, and total length showed significant relationships with stipe length. The length of the primary and longest blades gradually declined as stipe length increased above 125 mm. Zoosporangial sori were found on the blades of more than 70% of individuals with stipes longer than 125 mm, but on only 8% of individuals with stipes less than 125 mm long. Stipe length therefore seems to be an acceptable proxy for reproductive maturity. Another factor to consider, however, is that all specimens with zoosporangial sori, regardless of stipe length, had a dry weight of 80 g or more; thus, individual biomass may also be an important parameter influencing the initiation of reproduction.