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This work was funded by NERC studentship NE/I528185/1 awarded to W.R.G., NERC studentship NE/1492942/1 to B.T., NERC grant NE/N011716/1 awarded to J.W.B.R and A.B., and NERC grant NE/I013377/1 awarded to A.E.S. The interplay between ocean circulation and biological productivity affects atmospheric CO2 levels and marine oxygen concentrations. During the warming of the last deglaciation, the North Pacific experienced a peak in productivity and widespread hypoxia, with changes in circulation, iron supply and light limitation all proposed as potential drivers. Here we use the boron-isotope composition of planktic foraminifera from a sediment core in the western North Pacific to reconstruct pH and dissolved CO2 concentrations from 24,000 to 8,000 years ago. We find that the productivity peak during the Bølling–Allerød warm interval, 14,700 to 12,900 years ago, was associated with a decrease in near-surface pH and an increase in pCO2, and must therefore have been driven by increased supply of nutrient- and CO2-rich waters. In a climate model ensemble (PMIP3), the presence of large ice sheets over North America results in high rates of wind-driven upwelling within the subpolar North Pacific. We suggest that this process, combined with collapse of North Pacific Intermediate Water formation at the onset of the Bølling–Allerød, led to high rates of upwelling of water rich in nutrients and CO2, and supported the peak in productivity. The respiration of this organic matter, along with poor ventilation, probably caused the regional hypoxia. We suggest that CO2 outgassing from the North Pacific helped to maintain high atmospheric CO2 concentrations during the Bølling–Allerød and contributed to the deglacial CO2 rise. Postprint

A.J. Drury was funded by a Janet Watson studentship from Imperial College London. The late Miocene-early Pliocene was a time of global cooling and the development of modern meridional thermal gradients. Equatorial Pacific sea surface conditions potentially played an important role in this global climate transition, but their evolution is poorly understood. Here, we present the first continuous late Miocene-early Pliocene (8.0-4.4 Ma) planktic foraminiferal stable isotope records from eastern equatorial Pacific Integrated Ocean Drilling Program Site U1338, with a new astrochronology spanning 8.0-3.5 Ma. Mg/Ca analyses on surface dwelling foraminifera Trilobatus sacculifer from carefully selected samples suggest mean sea-surface-temperatures (SSTs) are ~27.8±1.1°C (1σ) between 6.4-5.5 Ma. The planktic foraminiferal δ18O record implies a 2°C cooling between 7.2-6.1 Ma and an up to 3°C warming between 6.1-4.4 Ma, consistent with observed tropical alkenone paleo-SSTs. Diverging fine-fraction-to-foraminiferal δ13C gradients likely suggest increased upwelling from 7.1-6.0 and 5.8-4.6 Ma, concurrent with the globally recognized late Miocene Biogenic Bloom. This study shows that both warm and asymmetric mean states occurred in the equatorial Pacific during the late Miocene-early Pliocene. Between 8.0-6.5 and 5.2-4.4 Ma, low east-west δ18O and SST gradients and generally warm conditions prevailed. However, an asymmetric mean climate state developed between 6.5-5.7 Ma, with larger east-west δ18O and SST gradients and eastern equatorial Pacific cooling. The asymmetric mean state suggests stronger trade winds developed, driven by increased meridional thermal gradients associated with global cooling and declining atmospheric pCO2 concentrations. These oscillations in equatorial Pacific mean state are reinforced by Antarctic cryosphere expansion and related changes in oceanic gateways (e.g., Central American Seaway/Indonesian Throughflow restriction). Publisher PDF

The small single-stranded DNA (ssDNA) bacteriophages of the subfamily Gokushovirinae were traditionally perceived as narrowly targeted, niche-specific viruses infecting obligate parasitic bacteria, such as Chlamydia. The advent of metagenomics revealed gokushoviruses to be widespread in global environmental samples. This study expands knowledge of gokushovirus diversity in the environment by developing a degenerate PCR assay to amplify a portion of the major capsid protein (MCP) gene of gokushoviruses. Over 500 amplicons were sequenced from 10 environmental samples (sediments, sewage, seawater and freshwater), revealing the ubiquity and high diversity of this understudied phage group. Residue-level conservation data generated from multiple alignments was combined with a predicted 3D structure, revealing a tendency for structurally internal residues to be more highly conserved than surface-presenting protein–protein or viral–host interaction domains. Aggregating this data set into a phylogenetic framework, many gokushovirus MCP clades contained samples from multiple environments, although distinct clades dominated the different samples. Antarctic sediment samples contained the most diverse gokushovirus communities, whereas freshwater springs from Florida were the least diverse. Whether the observed diversity is being driven by environmental factors or host-binding interactions remains an open question. The high environmental diversity of this previously overlooked ssDNA viral group necessitates further research elucidating their natural hosts and exploring their ecological roles.