Recent Directions in the Weisberg Lab

Transcription

1 Recent Directions in the Weisberg Lab by Robert H. Weisberg * Distinguished University Professor Professor of Physical Oceanography College of Marine Science, University of South Florida, St. Petersburg, FL January, 2015 * weisberg@usf.edu

2 Introduction Some 30 years into the College of Marine Science, Bob Weisberg s activities continue to be directed at describing and understanding the ocean circulation. All that has changed are the emphases and applications. Upon arrival in 1984, the emphasis was on the deep, equatorial oceans of the Atlantic and Pacific, with applications to ocean-atmosphere coupling, equatorially trapped waves, the El Nino Southern Oscillation and poleward heat flux. The emphases now are on the west Florida continental shelf and its estuaries, with applications to matters of more immediate societal concern. This transformation brings Weisberg full circle back toward the Narragansett Bay estuarine studies of his graduate student days at the University of Rhode Island. All my life s a circle sang Harry Chapin. Sverdrup, Johnson and Fleming, the venerable 1942 text no longer in print, established oceanography as a multidisciplinary science. Living marine resources, for instance, are a product of the environment in which they reside, and that environment derives it properties through the influx and efflux of mass, and the interactions that occur internally, i.e., the physics, chemistry, geology and biology of the system. One can study any of these aspects independently, but to gain insight on how the complex ocean system really works one need to study them interactively, and this requires collaborations. Like any jig-saw puzzle, one can work it alone, but it is usually more fun to do it with another, assuming they don t hog all of the border pieces. Such collaboration has been the approach of the Weisberg Lab. The following outlines a few recent projects and accomplishments. They are all predicated on a coordinated program of coastal ocean observing and modeling, albeit of the physical oceanography, but with applications of multidisciplinary nature. The coastal ocean, for our purposes, is defined as the continental shelf and the estuaries. It is literally where society meets the sea, where competing utilizations provide conflicts and stewardship requires understanding. Depletion of fisheries resources, pollution by spilled substances, blooms of harmful algae are some of the coastal ocean concerns, as are the destructive nature of hurricane storm surge and more mundane topics such as safe and efficient navigation by recreational and commercial boaters. Addressing these topics requires both observations and predictive capabilities through science-based models. Examples to be illustrated are as follows: 1) potential for Tampa Bay region damage by hurricane storm surge and waves, 2) harmful algae bloom prediction, 3) gag grouper recruitment 2

3 and 4) transport of Deepwater Horizon oil. These applications are all made possible through the coordination of observations with models, and collaborations with colleagues. The observations continue as part of our coastal ocean observing system activities, wherein we maintain a set of offshore buoys measuring ocean currents, temperature, salinity and surface meteorology, shorebased high frequency radars measuring surface currents and gliders (joint with our Ocean Technology Group) measuring sub-surface water properties. Our primary coastal ocean circulation model nests a very high resolution, unstructured grid model into a larger scale, Gulf of Mexico model run by the Naval Research Laboratory. In this way we downscale from the deep-ocean, across the continental shelf and into the estuaries (Zheng and Weisberg, 2012). The observations and models are available at Applications 1) Tampa Bay Storm Surge The combined population of Hillsborough and Pinellas Counties exceeds 2.2 million. What might happen if a hurricane such as Ivan (that hit the Florida Panhandle in 2004) were to made landfall near Tampa Bay? This was the subject of two papers (Weisberg and Zheng, 2009 and Huang et al., 2010) in which we took the observed Ivan winds and atmospheric pressure and redirected these to landfall just north of the bay. Figure 1 shows the combined surge and waves at a particular point in time sampled as the hypothetical storm transited eastward from Indian Rocks Beach. The results are alarming, particularly the waves, because (as became clear along the Mississippi coast in the aftermath of Hurricane Katrina) while surge may flood structures, it is generally the waves (in the absence of the strongest winds as in Hurricane Andrew), that destroy structures and cause death. We see in Figure 1 that large sections of populated land around Tampa Bay would be subjected to high water and destructive waves. Whereas resiliency for coastal properties is a popular discussion point, putting such concept into action is politically difficult. Studies like ours may at least provide some guidance. 2) Harmful Algae Bloom Prediction Blooms of the harmful algae, Karenia brevis, occur naturally along Florida s west coast. This slow growing dinoflagellate can, under certain conditions, out-compete faster growing diatoms, killing fish and subjecting coastal communities to toxic aerosols. Why this occurs in 3

4 some years and not in others now appears to be understood with respect to the coastal ocean circulation. Years in which the west Florida shelf is bathed in new inorganic nutrients that are upwelled across the shelf break are years without K. brevis blooms, and conversely. A 2010 case study (Weisberg et al., 2014a) concluded that both the ocean circulation physics and the organism biology are each necessary conditions for bloom development, but neither alone are sufficient conditions. Using the same logic as above, we subsequently (and successfully) predicted that there would not be a major K. brevis bloom in 2013 and that there would be one in K. brevis HABs provide an example of why coastal ocean ecology must be treated in a multidisciplinary manner. Note the deep chlorophyll maximum for July, 2010 in Figure 2, indicative of an offshore nutrient source. These glider-based observations, along with velocity profiles from moorings and surface velocity fields by HF-radar, are what we use for quantitatively gauging ocean circulation model performance, without which we would not be able to use the model to help diagnose how the coastal ocean system works. 3) Gag Grouper Recruitment Gag, the most prolific of the WFS reef fish, are known to spawn offshore and to begin their juvenile growth stage either in near-shore, or estuarine grass beds, but how they transit the shelf from their offshore spawning to near shore settlement sites was unknown. By combining coastal ocean circulation physics with fisheries biology, Weisberg et al. (2014b) accounted for observed juvenile observations in The circulation physics are similar to that explained in Weisberg et al. (2014a). Loop Current interactions along the shelf slope near the Dry Tortugas are again germane. If these occur in phase with spawning (primarily in late winter to early spring) and last long enough, then a particular year class may be successful. The 2007 year class provides a case in point. We tested both surface and near bottom transport route hypotheses and rejected the failed surface route hypothesis in favor of the successful near bottom route hypothesis. Further support for the near bottom transport route was gained from macroalgae of deep, hard bottom origin that were found to be co-located with the gag juveniles, plus other biochemical evidence. Simulated bottom route trajectories are shown in Figure 3. As with K. brevis HABs, gag recruitment is intimately tied to the coastal ocean circulation. 4) Did Hydrocarbons of Deepwater Horizon Origin Transit to the West Florida Shelf? 4

5 Our final example harkens back to the Deepwater Horizon oil spill (e.g., Liu et al., 2011) and the observation of fish lesions detected over the next year. Given the anomalously intense and prolonged upwelling that curtailed a K. brevis bloom in 2010, it was hypothesized that any hydrocarbons located within the water column, either dissolved or of sufficiently small particulate size to have effectively been dissolved, would have been carried from the north Florida shelf region, where surface oil was abundant, to the WFS, where no surface oil was detected. Weisberg et al. (2014c) explored this hypothesis and concluded that hydrocarbons of Deepwater Horizon origin did transit to the WFS sight unseen beneath the surface. Figure 4 shows a modeled tracer that matched the distribution of observed fish lesions, and limited liver chemistry samples offered additional evidence. By making reasonable assumptions of the initial tracer concentration and the subsequent dilution by advection and diffusion, we arrived at WFS tracer concentrations that may plausibly have affected reef fish. Concluding Remarks Oceanography is a multidisciplinary, applied science. Coastal ocean phenomena require observation and hypothesis testing before explanations may be found and predictions made. Determining how the coastal ocean system works sums up the goal of Weisberg s CMS lab. We pursue the physical oceanographic portion and rely upon collaborations for the other multidisciplinary aspects of this systems science. Most rewarding are the associations that develop. Sharing in the earlier CMS deep-ocean work are students and science associates: David Tang, Tom Weingartner, Chunzai Wang, Lin Qiao, Robert Helber and Jyotika Virmani. Continuing with the newer west Florida shelf work are students and science associates: Zhen Li, Ming-rui Zheng, Huijun Yang, Zhenjiang Li, Bryan Black, Eric Seigel, Ruoying He, Jyotika Virmani, Yonggang Liu, Alex Barth, Aida Alvera- Azcarate, Lianyuan Zheng, Yong Huang, Chudong Pan and our most recent students, Amanda Paiz, Ben O Loughlin and Jing Chen. Seagoing operations and laboratory computer and data management provide the underpinning to all that we do. Much is owed to many people beginning with Jack Hickman, Rick Cole, Patrick Smith and continuing with Jeff Donovan, Cliff Merz, Jay Law and Dennis Mayer. Continuity has been a very important part of our success, and without such excellent staff support none of our scientific work would be possible. 5

6 In my RESTORE Act testimony (before the House Transportation Committee in December 2011), I stated: You cannot fix it if you do not know how it works, and you cannot restore it if you do not know what it was to begin with. My ocean circulation group attempts to describe the west Florida shelf circulation, determine how it works and how it impacts important matters of societal concern. The environmental aspects of the RESTORE Act cannot be realized without such activities. Climate science may be fashionable, but It s your human environment that makes climate. Mark Twain. That is why we study what impacts us locally. Acknowledgments: Coastal ocean observing within the CMS was initiated in 1993 through a cooperative agreement with the United States Geological Survey. State of Florida support for a Coastal Ocean Monitoring and Prediction System (COMPS) was obtained in Various awards sustained these efforts through the present time, and external support now derives from the Southeast Coastal Ocean Observing Regional Association (SECOORA) as a pass through from NOAA Grant # NA11NOS for both moored buoy and HF-radar operations. Modeling support (now ended) was from the Gulf of Mexico Research Institute through the Florida State University administered Deep-C Program. We also benefit from a continuing relationship with the Florida Wildlife Research Institute. 6

7 References Huang, Y., R. H. Weisberg, and L. Zheng (2010). The coupling of surge and waves for an Ivanlike hurricane impacting the Tampa Bay, Florida region, J. Geophys. Res., 115, C12009, doi: /2009jc Liu, Y., A. MacFadyen, Z.-G. Ji, and R.H. Weisberg (Editors), (2011), Monitoring and Modeling the Deepwater Horizon Oil Spill: A Record-Breaking Enterprise, Geophysical Monograph Series, Vol. 195, 271 PP., ISSN: , ISBN AGU/geopress, Washington D.C. Weisberg, R. H., and L. Zheng (2008), Hurricane storm surge simulations comparing threedimensional with two-dimensional formulations based on an Ivan-like storm over the Tampa Bay, Florida region, J. Geophys. Res., 113, C12001, doi: /2008jc Weisberg, R.H., Zheng, L., Liu, Y., Lembke, C., Lenes, J.M., and Walsh, J.J. (2014a), Why a red tide was not observed on the West Florida Continental Shelf in Harmful Algae, 38, , doi: /j.hal Weisberg, R.H., Zheng, L., and Peebles, E. (2014b), Gag grouper larvae pathways on the West Florida Shelf, Cont. Shelf Res., doi /j.csr Weisberg, R.H., Zheng, L., Liu, Y., Murawski, S., Hu, C., and Paul, J. (2014c). Did Deepwater Horizon Hydrocarbons Transit to the West Florida Continental Shelf? Deep-Sea Res., Part II, doi: /j.dsr Zheng, L., and Weisberg, R.H. (2012). Modeling the west Florida coastal ocean by downscaling from the deep ocean, across the continental shelf and into estuaries. Ocean Modelling, 48,

8 Figure 1. The right hand panels show storm surge elevation relative to the land elevation (scale in meters given above) for different times during the storm s eastward transit from Indian Rocks Beach. These times are chosen to illustrate the worst flooding for the locations shown. The left hand panel shows the significant wave height (scale in meters given above). Note the 1 m wave heights across much of the land immediately adjacent to the bay. These are sufficiently high to destroy many residential structures. 8

9 Figure 2. Temperature, salinity, chlorophyll and CDOM sampled on an across shelf glider transect situated just north of Tampa Bay, FL during July 2010 (Adapted from Weisberg et al. 2014a). Note the effects of upwelling on the WFS water properties. 9

10 Figure 3. Model simulated near-bottom particle trajectories for particles initialized on the 40 m isobath, beginning (clockwise from the upper left hand panel) on April 9, April 11, April 13 and April 15, 2007, respectively (Adapted from Weisberg et al., 2014b). Particles of offshore, Big Bend origin arrived onshore where gag juveniles were observed. 10

11 Figure 4. Normalized near bottom tracer concentrations on July 15, 2010; July 30, 2010; August 15, 2010 and August 30, The normalized initial value for the tracer is 1.0, and the tracer concentration color bar is provided on a log10 scale. Thus the green region on the upper two panels corresponds to 0.40, and the dark blue and mid-range magenta regions on all panels correspond to 0.12 and 0.05, respectively. The grey region represents the lowest tracer concentration value plotted. It s location on the left hand side of the WFCOM model domain demarks the offshore extent of the inner model domain (adapted from Weisberg et al., 2014c). 11