Little islands recording global events: late Quaternary sea level history and paleozoogeography of Santa Barbara and Anacapa Islands, Channel Islands National Park, California

Marine terraces are common on the Pacific Coast of North America and record interglacial high-sea stands superimposed on either stable or tectonically rising crustal blocks. Despite many years of study of these landforms in southern California, little work on terraces has been conducted on the two smallest of the California Channel Islands, Santa Barbara Island (SBI) and Anacapa Island (ANA). Presented here are new field and laboratory data on the ages, paleontology, and sea level history of marine terraces of these two islands. On both islands, the lowest marine terraces have shoreline angle elevations of ~11 m above sea level. Amino acid geochronology shows that terrace deposits on both islands host fossils of two ages, one group dating to the ~120-ka high-sea stand and the other group likely dating to the ~100-ka high-sea stand. A mix of fossil ages is consistent with the paleontology as well, with SBI in particular showing a faunal assemblage that includes both extralimital southern and southward-ranging species (inferred to be from the ~120-ka high-sea stand) and extralimital northern and northward-ranging species (inferred to be from the ~100-ka high-sea stand). Fossil mixing from these two high-sea stands supports the hypothesis that glacial isostatic adjustment (GIA) processes have left a strong imprint on the geologic record of sea level history in southern California. Nevertheless, the elevations of these terraces and that of a low terrace on Santa Cruz Island indicate that modeled GIA estimates of paleo-sea level for the peak of the last interglacial period at ~120 ka could be too high. Future development of models of GIA effects on the Pacific Coast of North America will need to consider geologic records, such as those from SBI and ANA, in refining reconstructions of sea level history

Little islands recording global events: late Quaternary sea level history and paleozoogeography of Santa Barbara and Anacapa Islands, Channel Islands National Park, California

Marine terraces are common on the Pacific Coast of North America and record interglacial high-sea stands superimposed on either stable or tectonically rising crustal blocks. Despite many years of study of these landforms in southern California, little work on terraces has been conducted on the two smallest of the California Channel Islands, Santa Barbara Island (SBI) and Anacapa Island (ANA). Presented here are new field and laboratory data on the ages, paleontology, and sea level history of marine terraces of these two islands. On both islands, the lowest marine terraces have shoreline angle elevations of ~11 m above sea level. Amino acid geochronology shows that terrace deposits on both islands host fossils of two ages, one group dating to the ~120-ka high-sea stand and the other group likely dating to the ~100-ka high-sea stand. A mix of fossil ages is consistent with the paleontology as well, with SBI in particular showing a faunal assemblage that includes both extralimital southern and southward-ranging species (inferred to be from the ~120-ka high-sea stand) and extralimital northern and northward-ranging species (inferred to be from the ~100-ka high-sea stand). Fossil mixing from these two high-sea stands supports the hypothesis that glacial isostatic adjustment (GIA) processes have left a strong imprint on the geologic record of sea level history in southern California. Nevertheless, the elevations of these terraces and that of a low terrace on Santa Cruz Island indicate that modeled GIA estimates of paleo-sea level for the peak of the last interglacial period at ~120 ka could be too high. Future development of models of GIA effects on the Pacific Coast of North America will need to consider geologic records, such as those from SBI and ANA, in refining reconstructions of sea level history

A complex record of last interglacial sea-level history and paleozoogeography, Santa Rosa Island, Channel Islands National Park, California, USA

Studies of marine terraces and their fossils can yield important information about sea level history, tectonic uplift rates, and paleozoogeography, but some aspects of terrace history, particularly with regard to their fossil record, are not clearly understood. Marine terraces are well preserved on Santa Rosa Island, California, and the island is situated near a major marine faunal boundary. Two prominent low-elevation terraces record the ~80 ka (marine isotope stage [MIS] 5a) and ~120 ka (MIS 5e) high-sea stands, based on U-series dating of fossil corals and aminostratigraphic correlation to dated localities elsewhere in California and Baja California. Low uplift rates are implied by an interpretation of these ages, along with their elevations. The fossil assemblage from the ~120 ka (2nd) terrace contains a number of northern, cool-water species, along with several southern, warm-water species, a classic example of what has been called a thermally anomalous fauna. Low uplift rates in the late Pleistocene, combined with glacial isostatic adjustment (GIA) processes, could have resulted in reoccupation of the ~120 ka (MIS 5e), 2nd terrace during the ~100 ka (MIS 5c) high-sea stand, explaining the mix of warmwater (~120 ka?) and cool-water (~100 ka?) fossils in the terrace deposits. In addition, however, sea surface temperature (SST) variability during MIS 5e may have been a contributing factor, given that Santa Rosa Island is bathed at times by the cold California Current with its upwelling and at other times is subject to El Ni˜no warm waters, evident in the Holocene SST record. Study of an older, high-elevation marine terrace on the western part of Santa Rosa Island shows more obvious evidence of fossil mixing. Strontium isotope ages span a large range, from ~2.3 Ma to ~0.91 Ma. These analyses indicate an age range of ~500 ka at one locality and ~ 600 ka at another locality, interpreted to be due to terrace reoccupation and fossil reworking. Consideration of elevations and ages here also yield low, long-term uplift rates, which in part explains the potential for terrace reoccupation in the early Pleistocene. In addition, however, early Pleistocene glacial-interglacial cycles were of much shorter duration, linked to the ~41 ka obliquity cycle of orbital forcing, a factor that would also enhance terrace reoccupation in regions of low uplift rate. It is likely that other Pacific Coast marine terrace localities of early Pleistocene age, in areas with low uplift rates, also have evidence of fossil mixing from these processes, an hypothesis that can be tested in future studies

The marine terraces of Santa Cruz Island, California: Implications for glacial isostatic adjustment models of last-interglacial sea-level history

Glacial isostatic adjustment (GIA) models hypothesize that along coastal California, last interglacial (LIG, broadly from ~130 to ~115 ka) sea level could have been as high as +11 m to +13 m, relative to present, substantially higher than the commonly estimated elevation of +6 m. Areas with low uplift rates can test whether such models are valid. Marine terraces on Santa Cruz Island have previously been reported to occur at low (\u3c10 m) elevations, but ages of many such localities are not known. Using lidar imagery as a base, marine terraces on Santa Cruz Island were newly mapped, elevations were measured, fossils were collected for U-series dating (corals), strontium isotope compositions and amino acid geochronology (mollusks), and paleozoogeography (all taxa). Sr isotope compositions of mollusks from the highest of three marine terraces give ages of ~2.5 Ma to 1.9 Ma, along with Pliocene ages, fromshells interpreted to be reworked. U-series ages of corals fromthewestern part of the island indicate that low-elevation terraces north of the Santa Cruz Island fault correlate to the LIG. Where corals are lacking, amino acid ratios and faunal aspects support terrace correlation to the LIG high stand of sea. Elevations of most terrace localities north of the east-west trending Santa Cruz Island fault, in both thewestern and eastern parts of the island, range from5.75mto 8mabove sea level, well belowthe modeled paleo-sealevel range. Subsidence is ruled out as a mechanism for explaining the lower-than-modeled elevations, because higher-elevation terraces are present alongmuch of the Santa Cruz Island coast north of the fault, indicating longterm tectonic uplift. The low elevations of the LIG terrace fragments are, however, consistent with a low rate of uplift derived from the higher, ~2.5–1.9 Ma terrace. A number of other localities on the Pacific Coast, also dated to the LIG, have marine terrace elevations below the modeled level. GIA models may have overestimated last interglacial sea level by a substantial amount and need to be revised if used for forecasts for future sea-level rise

Tectonic influences on the preservation of marine terraces: Old and new evidence from Santa Catalina Island, California

The California Channel Islands contain some of the best geologic records of past climate and sea-level changes, recorded in uplifted, fossil-bearing marine terrace deposits. Among the eight California Channel Islands and the nearby Palos Verdes Hills, only Santa Catalina Island does not exhibit prominent emergent marine terraces, though the same terrace-forming processes that acted on the other Channel Islands must also have occurred on Santa Catalina. We re-evaluated previous researchers\u27 field evidence and examined new topographic, bathymetric, and stream-profile data in order to find possible explanations for the lack of obvious marine terrace landforms or deposits on the island today. The most likely explanation is associated with the island\u27s unresolved tectonic history, with evidence for both recent uplift and subsidence being offered by different researchers. Bathymetric and seismic reflection data indicate the presence of submerged terrace-like landforms from a few meters below present sea level to depths far exceeding that of the lowest glacial lowstand, suggesting that the Catalina Island block may have subsided, submerging marine terraces that would have formed in the late Quaternary. Similar submerged marine terrace landforms exist offshore of all of the other California Channel Islands, including some at anomalously great depths, but late Quaternary uplift is well documented on those islands. Therefore, such submarine features must be more thoroughly investigated and adequately explained before they can be accepted as definitive evidence of subsidence. Nevertheless, the striking similarity of the terrace-like features around Santa Catalina Island to those surrounding the other, uplifting, Channel Islands prompted us to investigate other lines of evidence of tectonic activity, such as stream profile data. Recent uplift is suggested by disequilibrium stream profiles on the western side of the island, including nickpoints and profile convexities. Rapid uplift is also indicated by the island\u27s highly dissected, steep topography and abundant landslides. A likely cause of uplift is a restraining bend in the offshore Catalina strike-slip fault. Our analysis suggests that Santa Catalina Island has recently experienced, and may still be experiencing, relatively rapid uplift, causing intense landscape rejuvenation that removed nearly all traces of marine terraces by erosion. A similar research approach, incorporating submarine as well as subaerial geomorphic data, could be applied to many tectonically active coastlines in which a marine terrace record appears to be missing

Electrical Anomalies Observed During DC3

The primary scientific goals of DC3 involved improving our understanding of the chemical impacts of thunderstorms and their anvils. However, the Colorado domain provided opportunities to study other interesting phenomena, including the potential impacts of smoke ingestion on convection and thunderstorms, electrification processes in smoke plumes and pyrocumulonimbus clouds, and the production of sprites by unconventional thunderstorm

Sea-level history during the Last Interglacial complex on San Nicolas Island, California: implications for glacial isostatic adjustment processes, paleozoogeography and tectonics

San Nicolas Island, California has one of the best records of fossiliferous Quaternary marine terraces in North America, with at least fourteen terraces rising to an elevation of ~270 m above present-day sea level. In our studies of the lowest terraces, we identified platforms at 38–36 m (terrace 2a), 33–28 m (terrace 2b), and 13–8 m (terrace 1). Uranium-series dating of solitary corals from these terraces yields three clusters of ages: ~120 ka on terrace 2a (marine isotope stage [MIS] 5.5), ~120 and ~100 ka on terrace 2b (MIS 5.5 and 5.3), and ~80 ka (MIS 5.1) on terrace 1.We conclude that corals on terrace 2b that date to ~120 ka were reworked from a formerly broader terrace 2a during the ~100 ka sea stand. Fossil faunas differ on the three terraces. Isolated fragments of terrace 2a have a fauna similar to that of modern waters surrounding San Nicolas Island. A mix of extralimital southern and extralimital northern species is found on terrace 2b, and extralimital northern species are on terrace 1. On terrace 2b, with its mixed faunas, extralimital southern species, indicating warmer than present waters, are interpreted to be from the ~120 ka high sea stand, reworked from terrace 2a. The extralimital northern species on terrace 2b, indicating cooler than present waters, are interpreted to be from the ~100 ka sea stand. The abundant extralimital northern species on terrace 1 indicate cooler than present waters at ~80 ka. Using the highest elevations of the ~120 ka platform of terrace 2a, and assuming a paleo-sea level of þ6 m based on previous studies, San Nicolas Island has experienced late Quaternary uplift rates of ~0.25–0.27 m/ka. These uplift rates, along with shoreline angle elevations and ages of terrace 2b (~100 ka) and terrace 1 (~80 ka) yield relative (local) paleo-sea level elevations of +2 to +6 m for the ~100 ka sea stand and –11 to –12 m for the ~80 ka sea stand. These estimates are significantly higher than those reported for the ~100 ka and ~80 ka sea stands on New Guinea and Barbados. Numerical models of the glacial isostatic adjustment (GIA) process presented here demonstrate that these differences in the high stands are expected, given the variable geographic distances between the sites and the former Laurentide and Cordilleran ice sheets. Moreover, the numerical results show that the absolute and differential elevations of the observed high stands provide a potentially important constraint on ice volumes during this time interval and on Earth structure

Polarimetric and Multi-Doppler Radar Observations of Electrified and Unelectrified Wildfire Smoke Plumes

Pyrocumulus clouds above three Colorado wildfires (Hewlett Gulch, High Park, and Waldo Canyon; all occurred during summer 2012) electrified and produced small intracloud discharges whenever the smoke plumes grew to high altitudes (over 10 km above mean sea level, or MSL). This occurred during periods of rapid wildfire growth, as indicated by the shortwave infrared channel on a geostationary satellite, as well as by incident reports. In the Hewlett Gulch case, the fire growth led to increased updrafts within the plume, as inferred by multiple Doppler radar syntheses, which led to the vertical development and subsequent electrification a life cycle as short as 30 minutes. The lightning, detected by a threedimensional lightning mapping network, was favored in highaltitude regions (~10 km MSL) containing modest reflectivities (25 dBZ and lower), ~0 dB differential reflectivity, and reduced correlation coefficient (~0.60.7). This indicated the likely presence of ice particles (crystals and aggregates, possibly rimed) mixed with ash. Though neither multipleDoppler nor polarimetric observations were available during the electrification of the High Park and Waldo Canyon plumes, their NEXRAD observations showed reflectivity structures consistent with Hewlett Gulch. In addition, polarimetric and multipleDoppler scanning of unelectrified High Park plumes indicated only irregularly shaped ash, and not ice, was present (i.e., reflectivities 5 dB, correlation < 0.4), and there was no broaching of the 10 km altitude. Based on these results, the electrification likely was caused by icebased processes that did not involve significant amounts of graupel. The results demonstrate the scientific value of multipleDoppler and polarimetric radar observations of wildfire smoke plumes including the ability to distinguish between regions of pure hydrometeors, regions of pure ash, and mixtures of both and also suggest a possible new application for lightning data in monitoring wildfires

Late Quaternary sea-level history and the antiquity of mammoths (\u3ci\u3eMammuthus exilis\u3c/i\u3e and \u3ci\u3eMammuthus columbi\u3c/i\u3e), Channel Islands National Park, California, USA

Fossils of Columbian mammoths (Mammuthus columbi) and pygmymammoths (Mammuthus exilis) have been reported from Channel Islands National Park, California. Most date to the last glacial period (Marine Isotope Stage [MIS] 2), but a tusk of M. exilis (or immature M. columbi) was found in the lowest marine terrace of Santa Rosa Island. Uranium-series dating of corals yielded ages from 83.8 ± 0.6 ka to 78.6 ± 0.5 ka, correlating the terrace withMIS 5.1, a time of relatively high sea level.Mammoths likely immigrated to the islands by swimming during the glacial periodsMIS 6 (~150 ka) orMIS 8 (~250 ka),when sea levelwas lowand the island–mainland distance was minimal, as during MIS 2. Earliest mammoth immigration to the islands likely occurred late enough in the Quaternary that uplift of the islands and the mainland decreased the swimming distance to a range that could be accomplished by mammoths. Results challenge the hypothesis that climate change, vegetation change, and decreased land area from sea-level rise were the causes of mammoth extinction at the Pleistocene/ Holocene boundary on the Channel Islands. Pre-MIS 2 mammoth populations would have experienced similar or even more dramatic changes at the MIS 6/5.5 transition

On the Electrification of Pyrocumulus Clouds

The electrification (or lack thereof) of pyrocumulus clouds is examined for several different wildfires that occurred during 20122013. For example, pyrocumulus clouds above three Colorado wildfires (Hewlett Gulch, High Park, and Waldo Canyon; all occurred during summer 2012) electrified and produced small intracloud discharges whenever the smoke plumes grew to high altitudes (over 10 km above mean sea level, or MSL). This occurred during periods of rapid wildfire growth, as indicated by the shortwave infrared channel on a geostationary satellite, as well as by incident reports. In the Hewlett Gulch case, the fire growth led to increased updrafts within the plume, as inferred by multipleDoppler radar syntheses, which led to the vertical development and subsequent electrification a life cycle as short as 30 minutes. The lightning, detected by a threedimensional lightning mapping network, was favored in highaltitude regions (~10 km MSL) containing modest reflectivities (25 dBZ and lower), ~0 dB differential reflectivity, and reduced correlation coefficient (~0.60.7). This indicated the likely presence of ice particles (crystals and aggregates, possibly rimed) mixed with ash. Though neither multipleDoppler nor polarimetric observations were available during the electrification of the High Park and Waldo Canyon plumes, their NEXRAD observations showed reflectivity structures consistent with Hewlett Gulch. In addition, polarimetric and multipleDoppler scanning of unelectrified High Park plumes indicated only irregularly shaped ash, and not ice, was present (i.e., reflectivities 5 dB, correlation < 0.4), and there was no broaching of the 10 km altitude. Based on these results, the electrification likely was caused by icebased processes that did not involve significant amounts of graupel. Results for pyrocumulus clouds above notable 2013 wildfires that also experienced rapid growth (e.g., Black Forest, Yarnell Hill, West Fork, Tres Lagunas, etc.) will be compared against the 2012 cases, with special emphasis on polarimetric NEXRAD and available lightning measurements, in order to better understand the physical processes responsible for pyrocumulus electrification