Dunbar Robert B.

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Dunbar

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Robert B.

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High apex predator biomass on remote Pacific islands

( 2006-09-06) Stevenson, Charlotte ; Katz, Laure S. ; Micheli, Fiorenza ; Block, Barbara A. ; Heiman, Kimberly W. ; Perle, Chris ; Weng, Kevin ; Dunbar, Robert B. ; Witting, Jan H.

On coral reefs in Palmyra—a central Pacific atoll with limited fishing pressure—total fish biomass is 428 and 299% greater than on reefs in nearby Christmas and Fanning Islands. Large apex predators –groupers, sharks, snappers, and jacks larger than 50 cm in length- account for 56% of total fish biomass in Palmyra on average, but only 7% and 3% on Christmas and Fanning. These biomass proportions are remarkably similar to those previously reported for the remote and uninhabited Northwest Hawaiian Islands (NWHI) and densely populated Main Hawaiian Islands (MHI), although Palmyra’s reefs are dominated in biomass by sharks (44% of the total), whereas the NWHI by jacks (39%). Herbivorous fish biomass was also greater on Palmyra than on Christmas and Fanning (343% and 207%, respectively). These results and previous findings indicate that remote, uninhabited islands support high levels of consumers, and highlight the importance of healthy coral reef ecosystems as reference points for assessment of human impacts and establishment of restoration goals.
Synergistic effects of iron and temperature on Antarctic phytoplankton and microzooplankton assemblages

(Copernicus Publications on behalf of the European Geosciences Union, 2009-12-21) Rose, J. M. ; Feng, Y. ; DiTullio, Giacomo R. ; Dunbar, Robert B. ; Hare, C. E. ; Lee, Peter A. ; Lohan, Maeve C. ; Long, Matthew C. ; Smith, Walker O. ; Sohst, Bettina M. ; Tozzi, S. ; Zhang, Y. ; Hutchins, David A.

Iron availability and temperature are important limiting factors for the biota in many areas of the world ocean, and both have been predicted to change in future climate scenarios. However, the impacts of combined changes in these two key factors on microbial trophic dynamics and nutrient cycling are unknown. We examined the relative effects of iron addition (+1 nM) and increased temperature (+4°C) on plankton assemblages of the Ross Sea, Antarctica, a region characterized by annual algal blooms and an active microbial community. Increased iron and temperature individually had consistently significant but relatively minor positive effects on total phytoplankton abundance, phytoplankton and microzooplankton community composition, as well as photosynthetic parameters and nutrient drawdown. Unexpectedly, increased iron had a consistently negative impact on microzooplankton abundance, most likely a secondary response to changes in phytoplankton community composition. When iron and temperature were increased in concert, the resulting interactive effects were greatly magnified. This synergy between iron and temperature increases would not have been predictable by examining the effects of each variable individually. Our results suggest the possibility that if iron availability increases under future climate regimes, the impacts of predicted temperature increases on plankton assemblages in polar regions could be significantly enhanced. Such synergistic and antagonistic interactions between individual climate change variables highlight the importance of multivariate studies for marine global change experiments.
Iron limitation of a springtime bacterial and phytoplankton community in the Ross Sea : implications for vitamin B12 nutrition

(Frontiers Media, 2011-08-15) Bertrand, Erin M. ; Saito, Mak A. ; Lee, Peter A. ; Dunbar, Robert B. ; Sedwick, Peter N. ; DiTullio, Giacomo R.

The Ross Sea is home to some of the largest phytoplankton blooms in the Southern Ocean. Primary production in this system has previously been shown to be iron limited in the summer and periodically iron and vitamin B12 colimited. In this study, we examined trace metal limitation of biological activity in the Ross Sea in the austral spring and considered possible implications for vitamin B12 nutrition. Bottle incubation experiments demonstrated that iron limited phytoplankton growth in the austral spring while B12, cobalt, and zinc did not. This is the first demonstration of iron limitation in a Phaeocystis antarctica-dominated, early season Ross Sea phytoplankton community. The lack of B12 limitation in this location is consistent with previous Ross Sea studies in the austral summer, wherein vitamin additions did not stimulate P. antarctica growth and B12 was limiting only when bacterial abundance was low. Bottle incubation experiments and a bacterial regrowth experiment also revealed that iron addition directly enhanced bacterial growth. B12 uptake measurements in natural water samples and in an iron fertilized bottle incubation demonstrated that bacteria serve not only as a source for vitamin B12, but also as a significant sink, and that iron additions enhanced B12 uptake rates in phytoplankton but not bacteria. Additionally, vitamin uptake rates did not become saturated upon the addition of up to 95 pM B12. A rapid B12 uptake rate was observed after 13 min, which then decreased to a slower constant uptake rate over the next 52 h. Results from this study highlight the importance of iron availability in limiting early season Ross Sea phytoplankton growth and suggest that rates of vitamin B12 production and consumption may be impacted by iron availability.
Nitrate and phosphate from various depths throughout the water column inside and outside a kelp forest near the Monterey Peninsula, California, USA from June to August 2018 and 2019

(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2022-08-23) Nickols, Kerry J. ; Dunbar, Robert B.

This dataset includes nitrate and phosphate from various depths throughout the water column collected at mooring sites inside and outside a kelp forest near the Monterey Peninsula, California, USA. Data were collected from June to August in 2018 and 2019. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/863702
Water level and seafloor temperature from Onset HOBO U20L loggers deployed on the seafloor adjacent to instrument moorings inside and outside of kelp forests near the Monterey Peninsula, California, USA from June to August 2018 and 2019

(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2022-03-30) Nickols, Kerry J. ; Dunbar, Robert B.

These data are from Onset HOBO U20L data loggers recording at 1-minute intervals deployed on the seafloor from June to August in 2018 and 2019. The HOBO loggers were deployed adjacent to instrument moorings inside and outside of kelp forests near the Monterey Peninsula, California, USA. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/864720
Nighttime surface chlorophyll-a concentrations at the MBARI OA1 Buoy (36° 37.373’ N, 121 ° 54.000’ W) from June to October 2018

(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2020-10-16) Hirsh, Heidi ; Nickols, Kerry J. ; Takeshita, Yuichiro ; Traiger, Sarah ; Monismith, Stephen G. ; Mucciarone, David ; Dunbar, Robert B.

Nighttime surface chlorophyll-a concentrations at the MBARI OA1 Buoy (36° 37.373’ N, 121 ° 54.000’ W) from June to October 2018 For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/822494
pH measured in situ over depth in the kelp forest (36° 37.3’ N, 121° 54.1’ W) recorded in July 2018.

(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2020-10-16) Hirsh, Heidi ; Nickols, Kerry J. ; Takeshita, Yuichiro ; Traiger, Sarah ; Monismith, Stephen G. ; Mucciarone, David ; Dunbar, Robert B.

pH measured in situ over depth in the kelp forest (36° 37.3’ N, 121° 54.1’ W) recorded in July 2018. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/826162
Surface irradiance measured on the roof of the Monterey Bay Aquarium (36.62 °N, 121.90 °W) from June to October 2018

(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2020-10-16) Hirsh, Heidi ; Nickols, Kerry J. ; Takeshita, Yuichiro ; Traiger, Sarah ; Monismith, Stephen G. ; Mucciarone, David ; Dunbar, Robert B.

Surface irradiance measured on the roof of the Monterey Bay Aquarium (36.62 °N, 121.90 °W) from June to October 2018. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/822517
Temperature data from Onset HOBO U22 loggers deployed at various depths on instrument moorings inside and outside of kelp forests near the Monterey Peninsula, California, USA from June to August 2018 and 2019

(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2022-04-04) Nickols, Kerry J. ; Dunbar, Robert B.

These data are from Onset HOBO U22 data loggers recording at 1-minute intervals deployed at various depths on instrument moorings from June to August in 2018 and 2019. Moorings were located inside and outside of a kelp forests near the Monterey Peninsula, California, USA. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/864813
Cross-shore and alongshore velocity inside the kelp forest at Hopkins Marine Station (36° 37.297’ N, 121° 54.102’ W) recorded between June and October, 2018.

(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2020-10-16) Hirsh, Heidi ; Nickols, Kerry J. ; Takeshita, Yuichiro ; Traiger, Sarah ; Monismith, Stephen G. ; Mucciarone, David ; Dunbar, Robert B.

Cross-shore and alongshore velocity inside the kelp forest at Hopkins Marine Station (36° 37.297’ N, 121° 54.102’ W) recorded between June and October, 2018. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/826431
Dissolved oxygen and temperature from PME miniDOT sensors recording at 1-minute intervals at various depths on instrument moorings inside and outside of kelp forests near the Monterey Peninsula, California, USA from June to August 2018 and 2019

(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2022-03-30) Nickols, Kerry J. ; Dunbar, Robert B.

These data are from PME miniDOT sensors recording dissolved oxygen and temperature at 1-minute intervals at various depths on instrument moorings from June to August in 2018 and 2019. Data were collected at mooring sites inside and outside of kelp forests near the Monterey Peninsula, California, USA. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/864402
Kelp forest mooring DIC, TA, pCO2, and aragonite saturation state estimations inside the kelp canopy (36° 37.297’ N, 121° 54.102’ W.) at Hopkins Marine Station, recorded between June and October 2018.

(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2020-10-16) Hirsh, Heidi ; Nickols, Kerry J. ; Takeshita, Yuichiro ; Traiger, Sarah ; Monismith, Stephen G. ; Mucciarone, David ; Dunbar, Robert B.

Kelp forest mooring DIC, TA, pCO2, and aragonite saturation state estimations inside the kelp canopy (36° 37.297’ N, 121° 54.102’ W.) at Hopkins Marine Station, recorded between June and October 2018. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/823008
Temperature data from SeaBird SBE56 sensors deployed at various depths on instrument moorings inside and outside of kelp forests near the Monterey Peninsula, California, USA from June to August 2018 and 2019

(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2022-04-04) Nickols, Kerry J. ; Dunbar, Robert B.

These data are from SeaBird SBE56 sensors recording at 1-minute intervals deployed at various depths on instrument moorings from June to August in 2018 and 2019. Moorings were located inside and outside of kelp forests near the Monterey Peninsula, California, USA. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/865073
Dissolved Inorganic Carbon measured in situ over depth in the kelp forest (36° 37.3’ N, 121° 54.1’ W) recorded in July 2018.

(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2020-10-16) Hirsh, Heidi ; Nickols, Kerry J. ; Takeshita, Yuichiro ; Traiger, Sarah ; Monismith, Stephen G. ; Mucciarone, David ; Dunbar, Robert B.

Dissolved Inorganic Carbon measured in situ over depth in the kelp forest (36° 37.3’ N, 121° 54.1’ W) recorded in July 2018. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/826200
Reproducibility of Ba/Ca variations recorded by northeast Pacific bamboo corals

(John Wiley & Sons, 2017-09-13) Serrato Marks, Gabriela ; LaVigne, Michèle ; Hill, Tessa M. ; Sauthoff, Wilson ; Guilderson, Thomas P. ; Roark, E. Brendan ; Dunbar, Robert B. ; Horner, Tristan J.

Trace elemental ratios preserved in the calcitic skeleton of bamboo corals have been shown to serve as archives of past ocean conditions. The concentration of dissolved barium (BaSW), a bioactive nutrientlike element, is linked to biogeochemical processes such as the cycling and export of nutrients. Recent work has calibrated bamboo coral Ba/Ca, a new BaSW proxy, using corals spanning the oxygen minimum zone beneath the California Current System. However, it was previously unclear whether Ba/Cacoral records were internally reproducible. Here we investigate the accuracy of using laser ablation inductively coupled plasma mass spectrometry for Ba/Cacoral analyses and test the internal reproducibility of Ba/Ca among replicate radial transects in the calcite of nine bamboo corals collected from the Gulf of Alaska (643–720 m) and the California margin (870–2054 m). Data from replicate Ba/Ca transects were aligned using visible growth bands to account for nonconcentric growth; smoothed data were reproducible within ~4% for eight corals (n = 3 radii/coral). This intracoral reproducibility further validates using bamboo coral Ba/Ca for BaSW reconstructions. Sections of the Ba/Ca records that were potentially influenced by noncarbonate bound Ba phases occurred in regions where elevated Mg/Ca or Pb/Ca and coincided with anomalous regions on photomicrographs. After removing these regions of the records, increased Ba/Cacoral variability was evident in corals between ~800 and 1500 m. These findings support additional proxy validation to understand BaSW variability on interannual timescales, which could lead to new insights into deep sea biogeochemistry over the past several centuries.
Discrete seawater samples collected at the surface, 1 m below the surface, and 1 m above the bottom two times a week at each mooring (Kelp and Outside) from June 12, 2018 to August 3, 2018.

(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2020-10-16) Hirsh, Heidi ; Nickols, Kerry J. ; Takeshita, Yuichiro ; Traiger, Sarah ; Monismith, Stephen G. ; Mucciarone, David ; Dunbar, Robert B.

Discrete seawater samples collected at the surface, 1 m below the surface, and 1 m above the bottom two times a week at each mooring (Kelp and Outside) from June 12, 2018 to August 3, 2018. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/826410
CTD casts paired with bi-weekly water sampling events at instrument mooring sites near the Monterey Peninsula, California, USA from June to August 2018 and 2019

(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2022-08-23) Nickols, Kerry J. ; Dunbar, Robert B.

These data were obtained from CTD casts paired with bi-weekly water sampling events at instrument mooring sites near the Monterey Peninsula, California, USA. Data were collected from June to August in 2018 and 2019. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/863637
Early season depletion of dissolved iron in the Ross Sea polynya : implications for iron dynamics on the Antarctic continental shelf

(American Geophysical Union, 2011-12-15) Sedwick, Peter N. ; Marsay, Christopher M. ; Sohst, Bettina M. ; Aguilar-Islas, Ana M. ; Lohan, Maeve C. ; Long, Matthew C. ; Arrigo, Kevin R. ; Dunbar, Robert B. ; Saito, Mak A. ; Smith, Walker O. ; DiTullio, Giacomo R.

The Ross Sea polynya is among the most productive regions in the Southern Ocean and may constitute a significant oceanic CO2 sink. Based on results from several field studies, this region has been considered seasonally iron limited, whereby a “winter reserve” of dissolved iron (dFe) is progressively depleted during the growing season to low concentrations (~0.1 nM) that limit phytoplankton growth in the austral summer (December–February). Here we report new iron data for the Ross Sea polynya during austral summer 2005–2006 (27 December–22 January) and the following austral spring 2006 (16 November–3 December). The summer 2005–2006 data show generally low dFe concentrations in polynya surface waters (0.10 ± 0.05 nM in upper 40 m, n = 175), consistent with previous observations. Surprisingly, our spring 2006 data reveal similar low surface dFe concentrations in the polynya (0.06 ± 0.04 nM in upper 40 m, n = 69), in association with relatively high rates of primary production (~170–260 mmol C m−2 d−1). These results indicate that the winter reserve dFe may be consumed relatively early in the growing season, such that polynya surface waters can become “iron limited” as early as November; i.e., the seasonal depletion of dFe is not necessarily gradual. Satellite observations reveal significant biomass accumulation in the polynya during summer 2006–2007, implying significant sources of “new” dFe to surface waters during this period. Possible sources of this new dFe include episodic vertical exchange, lateral advection, aerosol input, and reductive dissolution of particulate iron.
Data from moored instruments (pH, dissolved oxygen, temperature, salinity, PAR, pressure) at 9 depths outside and inside the kelp canopy at Hopkins Marine Station, recorded between June and October 2018.

(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2020-10-16) Hirsh, Heidi ; Nickols, Kerry J. ; Takeshita, Yuichiro ; Traiger, Sarah ; Monismith, Stephen G. ; Mucciarone, David ; Dunbar, Robert B.

Data from moored instruments (pH, dissolved oxygen, temperature, salinity, PAR, pressure) at 9 depths outside (36° 37.342’ N, 121° 54.049’ W) and inside the kelp canopy (36° 37.297’ N, 121° 54.102’ W.) at Hopkins Marine Station, recorded between June and October 2018. The tidal depth of the kelp canopy mooring ranges from 8 to 11 meter. The outside mooring is located 115m north and offshore from the kelp forest, the tidal range is 16 to 9 meters. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/822549
Mid-Holocene Antarctic sea-ice increase driven by marine ice sheet retreat

(European Geosciences Union, 2021-01-05) Ashley, Kate E. ; McKay, Robert ; Etourneau, Johan ; Jimenez-Espejo, Francisco J. ; Condron, Alan ; Albot, Anna ; Crosta, Xavier ; Riesselman, Christina ; Seki, Osamu ; Massé, Guillaume ; Golledge, Nicholas ; Gasson, Edward ; Lowry, Daniel P. ; Barrand, Nicholas E. ; Johnson, Katelyn ; Bertler, Nancy ; Escutia, Carlota ; Dunbar, Robert B. ; Bendle, James A.

Over recent decades Antarctic sea-ice extent has increased, alongside widespread ice shelf thinning and freshening of waters along the Antarctic margin. In contrast, Earth system models generally simulate a decrease in sea ice. Circulation of water masses beneath large-cavity ice shelves is not included in current Earth System models and may be a driver of this phenomena. We examine a Holocene sediment core off East Antarctica that records the Neoglacial transition, the last major baseline shift of Antarctic sea ice, and part of a late-Holocene global cooling trend. We provide a multi-proxy record of Holocene glacial meltwater input, sediment transport, and sea-ice variability. Our record, supported by high-resolution ocean modelling, shows that a rapid Antarctic sea-ice increase during the mid-Holocene (∼ 4.5 ka) occurred against a backdrop of increasing glacial meltwater input and gradual climate warming. We suggest that mid-Holocene ice shelf cavity expansion led to cooling of surface waters and sea-ice growth that slowed basal ice shelf melting. Incorporating this feedback mechanism into global climate models will be important for future projections of Antarctic changes.

Dunbar Robert B.

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