ARISE

Description

Rapid environmental change is already affecting Arctic ecosystems. The Arctic Ocean is now adjusting to new, warmer conditions. Understanding the ecosystem response in detail is essential if the projections of future impacts are to be reliable. This can be gauged by identifying exactly how Arctic food webs are changing now and in the recent past.

Ecosystems

Ecosystems are communities of organisms that interact with each other and their environment. They are often considered in terms of food webs or chains, which describe the interactions between different organisms and their relative hierarchies, known as tropic position. Ocean ecosystems provide key services, such as nutrition, control of climate, support of nutrient cycling and have cultural significance for certain communities. It is thus important that we understand how changes to the environment reshape ecosystems in order to manage climate change impacts.

Environmental change in the Arctic

The Arctic Ocean is already being heavily impacted by climate change. It is warming faster than any other ocean region and as it absorbs fossil fuel emissions, it is gradually acidifying. Arctic sea ice is declining by 10% per decade. This affects the availability of sea ice habitats for organisms from plankton to mammals and modifies the ocean environment. Finally, the Arctic is affected by changes in the magnitude of water movement to and from the Pacific and Atlantic Oceans and composition of these waters. Thus Arctic ecosystems are being impacted by multiple concurrent stressors and must adapt.

Response of Arctic ecosystems to change

To understand how Arctic ecosystems will evolve in response to multiple stressors, it is crucial to evaluate the effects of on-going change. Often these questions are tackled by studies that focus on a specific ecosystem in one location and document the various components of the food chain. However the Arctic is diverse, with a wide range of environments that are responding to unique stressors differently. We require a new approach that can provide information on Arctic ecosystems from a pan-Arctic perspective over decadal timescales.

Ecosystems

Ecosystems are communities of organisms that interact with each other and their environment. They are often considered in terms of food webs or chains, which describe the interactions between different organisms and their relative hierarchies, known as tropic position. Ocean ecosystems provide key services, such as nutrition, control of climate, support of nutrient cycling and have cultural significance for certain communities. It is thus important that we understand how changes to the environment reshape ecosystems in order to manage climate change impacts.

Environmental change in the Arctic

The Arctic Ocean is already being heavily impacted by climate change. It is warming faster than any other ocean region and as it absorbs fossil fuel emissions, it is gradually acidifying. Arctic sea ice is declining by 10% per decade. This affects the availability of sea ice habitats for organisms from plankton to mammals and modifies the ocean environment. Finally, the Arctic is affected by changes in the magnitude of water movement to and from the Pacific and Atlantic Oceans and composition of these waters. Thus Arctic ecosystems are being impacted by multiple concurrent stressors and must adapt.

Response of Arctic ecosystems to change

To understand how Arctic ecosystems will evolve in response to multiple stressors, it is crucial to evaluate the effects of on-going change. Often these questions are tackled by studies that focus on a specific ecosystem in one location and document the various components of the food chain. However the Arctic is diverse, with a wide range of environments that are responding to unique stressors differently. We require a new approach that can provide information on Arctic ecosystems from a pan-Arctic perspective over decadal timescales.

Measuring change

To effectively monitor changes to pan-Arctic ecosystems requires tracers that focus on key ecosystem components and provide quantitative information on ecosystem structure. Our goal is to respond to this challenge. We will focus simultaneously on the base of the food chain, controlled by the activity of marine phytoplankton, and key Arctic predators, harp and ringed seals. Seals are excellent candidates to monitor the food web due to their pan-Arctic distribution and foraging behaviour, which means they are exposed to the changing environment. This will provide information for management and conservation of ecosystem services

The isoscape

Nitrogen and carbon stable isotopes are often used to examine ecosystems as they are modified during trophic transfer up the food chain. Hence, they can quantify seal trophic position and food chain length, key determinants of ecosystem structure. Crucial in this context however is the isotope value of the base of the food web, known as the isoscape, which is itself affected by a range of environmental characteristics and fluctuates in space and time. Equally, by virtue of changing migration patterns, seals themselves may feed on similar prey in different isoscapes, which would affect the interpretation of ecosystem structure from stable isotopes. These are the major challenges in using stable isotopes in complex ecosystems that are undergoing change.

Use of biomarkers

We will link stable isotopes to novel tracers of the food web, known as biomarkers. When these tracers are compared against observations of the shifting isoscape and data on seal foraging, they permit seals to be used to monitor the Arctic ecosystem by quantifying their trophic position and overall food chain length. Via a range of observational platforms, our new food web tracers will be mechanistically linked to the spatial and seasonal trends in the Arctic isoscape and seal behaviour. By then combining historical observations from around the Arctic basin with state-of-the-art ocean and seal population modelling, we can quantify past and future changes in Arctic ecosystems. This will provide information on past changes to Arctic ecosystems, but also put in place an approach that can be used to monitor future changes and aid in the management and conservation of ecosystem services.

ARISE Objectives

Our project objectives will put into place a set of new tools that are able to detect pan-Arctic modifications to ecosystems and evaluate past and future change across a diverse set of Arctic environments. We deliberately avoid detailed ecosystem studies at a single site, as they cannot provide the large-scale vision necessary to properly manage the impact of on-going environmental change across the Arctic. Our approach overcomes this limitation by combining pan-Arctic historical and contemporary observations with traditional isotope and novel biomarkers as food web tracers to gain a complete understanding of how environmental change affects both the base of the food web and two Arctic seal species, considered ‘indicator species’. This will provide new insights into variations in seal trophic position and food chain length over wide space and time scales.

We have three hypotheses that will be tested by three objectives linked by modular work plans. Our objectives are designed around a stepwise accumulation of understanding. First we will gain observational constraints on how environmental variability affects the isotope composition of the base of the food web, termed the ‘isoscape’. Next, we will combine data on seal foraging and migration to understand how variability in the isoscape is reflected in biomarker signals in seals. Then, we will exploit historical observations and link our new understanding to ocean and seal population models to provide a broad picture of factors driving past and contemporary Arctic ecosystem change. Finally, we will quantitatively assess the conservation and management implications of our results, with strong links to stakeholders and policy makers.

Objective 1

Objective 1 will constrain the spatial and seasonal variability of the isoscape and determine the local and external drivers of its variability at pan-Arctic scales. This will be achieved by combining seasonal pan-Arctic observations of the nitrogen and carbon stable isotope composition of nutrients, carbon and the isoscape during NERC and project partner cruises (including riverine end members), with physical characteristics of the water masses, remote sensing datasets and targeted model experiments using a state of the art biogeochemical model to isolate the driving mechanisms.

Objective 2

Objective 2 will determine the sensitivity of the food web tracers in seals to the stable isotope composition at the base of the food web and the impact on inferred trophic position. This will be achieved by a combination of seasonal and spatial sampling of the isoscape and seal trophic position. It will also employ telemetry to constrain the areal extent of the isoscape experienced by harp seals, which, when linked to remote sensing datasets and hydrography from tags, will isolate the drivers behind their migration and foraging patterns.

Objective 3

Objective 3 will quantify how decadal changes in climate affect the attribution of variations in the food web tracer signals recorded by seals to changes in the isoscape in the context of local and global change at the base of the food web. We will examine novel pan-Arctic datasets of seal tissues collected since the 1950s and long-term model simulations in collaboration with NOC and the UK Earth System Model, which will also be linked to historical telemetry data on seal migration and behaviour.

Objective 4

Objective 4 will quantify the effects of environmental change on seal populations. We will combine environmental data sets from remote sensing and modelling outputs, and inferences about food web changes from biomarker work to model impacts on vital rates of seals and seal populations. This will enable practical links to management and policy makers towards informing future decision-making, as part of our Pathways to Impact.