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Traditionally, deep-sea ecosystems have been considered to be insulated from the effects of modern climate change. Yet, with the recognition of the importance of food supply from the surface ocean and deep-sea currents to sustaining these systems, the potential for rapid response of benthic systems to climate change is gaining increasing attention. North Atlantic benthic responses to past climate change have been well-documented using marine sediment cores on glacial-interglacial timescales, and ocean sediments have also begun to reveal that planktic species assemblages are already being influenced by global warming. However, very few ecological time-series exist for the deep ocean covering the Holocene-through-industrial era. Here, we use benthic and planktic foraminifera found in Northeast Atlantic (EN539-MC16-A/B and RAPID-17-5P), Northwest Atlantic (KNR158-4-10MC and KNR158-4-9GGC) and Labrador Sea (RAPID-35-25B and RAPID-35-14P) sediments to show that, in locations beneath areas of major North Atlantic surface water change, benthic ecosystems have also changed significantly over the industrial era relative to the Holocene. We find that the response of the benthos is dependent on changes in the surface ocean near to the study sites. Our work highlights the spatial heterogeneity of these benthic ecosystem changes and therefore the need for local-regional scale modelling and observations to better understand responses to deep-sea circulation changes and modern surface climate change.

In the last decades, many studies have attempted to analyse the factors that may favour the evolution of cooperation. Among unrelated individuals, cooperation is expected to occur when partners exchange altruistic acts one another (i.e., reciprocity) or when the donor of an altruistic act may obtain secondary benefits from the act (e.g., increased reputation). The iterated prisoner's dilemma (IPD) is frequently used to analyse cooperation between two players. In this game, cooperation is constantly at risk of exploitation. Therefore, previous knowledge of the other player's attitude towards cooperation may positively affect an individual's decision to cooperate during the game. In various social species (including humans), group members may form friendly relationships that reduce uncertainty about the partner response and increase the mutual exchange of benefits. In light of this, we analysed whether humans cooperate more when playing an IPD with a friend than with a stranger. Each subject played an IPD twice, with a friend and a stranger, and had £10 per round to donate or not to the other player. Our results evidenced that humans cooperate more with, and donate more money to the other player when playing with a friend than with a stranger. Moreover, in game two subjects playing with unfamiliar players followed a raise the stakes strategy (RTS), i.e. they donated more money as the game progressed. The sense of trust in the other player's willingness to reciprocate the altruistic act is probably an important pre-requisite favouring cooperation and it may explain the differences between friends and unfamiliar players. The use of a RTS strategy in game two, however, indicates that subjects were attempting to increase the level of cooperation with unfamiliar players. These findings are consistent with the observation that friendship (and the capacity to build cooperative relationships) may be beneficial to individuals in many social animals and in humans.

Traditionally, deep-sea ecosystems have been considered to be insulated from the effects of modern climate change, but with the recognition of the importance of food supply from the surface ocean and deep-sea currents to sustaining these systems, the potential for rapid response of benthic systems to climate change is gaining increasing attention. However, very few ecological time-series exist for the deep ocean covering the twentieth century. Benthic responses to past climate change have been well-documented using marine sediment cores on glacial-interglacial timescales, and ocean sediments have also begun to reveal that planktic species assemblages are already being influenced by global warming. Here, we use benthic foraminifera found in mid-latitude and subpolar North Atlantic sediment cores to show that, in locations beneath areas of major surface water change, benthic ecosystems have also changed significantly over the last ~150 years. The maximum benthic response occurs in areas which have seen large changes in surface circulation, temperature and/or productivity. We infer that the observed surface-deep ocean coupling is due to changes in the supply of organic matter exported from the surface ocean and delivered to the seafloor. The local-to-regional scale nature of these changes highlights that accurate projections of changes in deep-sea ecosystems will require (1) increased spatial coverage of deep-sea proxy records and, (2) models capable of adequately resolving these relatively small-scale oceanographic features.